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high as the hind ones, and the higher the better, because their motion would be so much slower on their axles, and, consequently, the friction proportionally diminished.
"There is an inconvenience which attends the usual method of loading carriages; for when a carriage is loaded equally on both axles, the fore axle must endure so much more friction. However, the carriers put the heaviest part of the load upon the fore axle, which not only makes the friction greatest where it ought to be least, but also presseth the fore wheels deeper into the ground than the hind wheels, although the fore wheels, being less than the hind ones, are with so much the greater difficulty drawn.
"By throwing the greatest part of the load on the small wheels the draught becomes doubly severe on the horses, who thus unnecessarily suffer for the ignorance and folly of man."
Extract from Ferguson's Lectures on Mechanics. ■ Edition 1806.
"Large fore wheels are advantageous, both in horizontal and inclined planes.
"It must naturally occur to every person reflecting upon this subject, that the axletrees should be straight, and the wheels perfectly parallel.
"In some carriages which we have examined, where the wheels were only 4 feet 6 inches in diameter, the distance of the wheels at top was fully 6 feet, and their distance below only 4 feet 8 inches: by this foolish practice the very advantages which may be derived from the concavity of the wheels are completely taken away.
"The direction of the traces should be inclined to the horizon when the horse is at rest, in order that it may be horizontal when he lowers his breast and exerts his utmost force."
Extract from a Pamphlet entitled " Cursory Remarks on Wheel Carriages" by Mr. John Cook, of Liquorpond-street, Coach Builder.
"With smaller wheels before than behind, the disadvantage is increased in proportion to the smallness of them ; so that if small fore wheels must be used, the weight ought to be brought nearer to the hind ones."—p. 15.
"From the before-mentioned cause (the great weight over the fore wheels), the fore wheels are pressed so forcibly into the ground, particularly in bad weather, that they are in a continual hole, while the hind ones, capable of taking the greatest weight, have the least; which, added to the immense friction from dished wheels, together with the present favourite system of curtailing their height, and of oblique traction, nearly doubles the draught."—p. 24.
In applying the principles here laid down, it will be proper not to carry them further than experience will justify, and only to approximate, as much as possible, the construction of a coach to these principles; and therefore, as experience shows that a wheel of the height of 4 feet 8 inches affords verygreat assistance in drawing carriages, in consequence of the length of its spokes, or leverage, and can be made of great strength, without being very heavy, it is proposed in the plan now submitted for consideration that the hind wheels of a coach should be of this height.
The risk of overturning being greater or less, according to the height of a coach from the ground, it is proposed, in order to keep the body as low as possible, to fix the hind end of the perch below the hind axle.
As the running of a coach, whether well or ill, depends very much on the way in which the hind wheels follow the fore ones, and as this depends in some degree on the length of the perch, the perch should be as short as it can be made with safety, with regard to the greater tendency of a coach with a short perch to overturn than with a long one. On these considerations it is proposed that the length of the perch, between the centres of the fore and hind axles, should be 6 feet.
From what has been said about wheels, it is clear that the fore wheels should be as high as the hind ones; but as such a height would interfere with the turning of a coach, and as fore wheels as high as 46 inches are already, in some cases, in use, it is proposed that the fore wheels should be of this height. It is probable that the further trial of wheels of this height will show that still higher ones may be conveniently used.
As a space of 7 inches should be allowed for the play of the springs, the bottom of the hind boot should be 7 inches above the axle.
Most stage-coaches at present have the axles 4 feet, or 4 feet 1 inch between the collars, and the arms are set in such a manner that the wheels are 4 inches wider asunder at top than at bottom. This drooping of the arms adds very much to the draught. The principal reason in support of this dish-form given to wheels is that it enables the wheels to bear sudden lateral thrust. If a wheel with spokes perpendicular to the nave fall into a rut, and if in that situation the nave be pushed outwards by the swing of the carriage, the chances are that it may be thrust through altogether, and the spokes be forced out both from the nave and from the fellies; whereas in a dished wheel the nave cannot yield outwards until the shock be great enough to burst the tire by the extension of the spokes. Another practical advantage of a moderate degree of dishing is, that it admits of the spokes yielding a little when the tire or ring is first put on, and retaining their tendency to spring back to their first position, by which the fellies are made to continue to bear against the tire, even after it has been lengthened by the blows it gets in running over hard pavement.
The fore and hind axles should be of the same length. The arms should taper one quarter of an inch, and be slightly bent, so as to bring an upright spoke. The fore and hind wheels should rest on the ground 4 feet 8 inches asunder from out to out. The dish given to the wheels should be so adjusted as to secure the following of the hind wheels in the track of the fore ones.
Another inconvenience which arises from a perfectly upright wheel is the throwing of the road mud into the coach-windows and on to the roof.
The thickness and length of the bearing part of the axle should also be attended to; in heavy stagecoaches the arms are made 2| inches in diameter, and 11 inches long. If the arms be made of the best case-hardened iron, and perfectly cylindrical, 2 inches in diameter is sufficient, according to mechanical principles, with a bearing of 7 inches. The total length of the arms should, however, be 10 inches, 3 inches of it being hollowed out for holding oil or grease.
The proper width of the tires of wheels must be determined by experiment. That there is some certain width of tire which will produce the least resistance to draught cannot be denied, but what that width should be is at present uncertain. There is one thing, however, very clear, namely, that, theoretically, the narrow wheel produces the least resistance on good roads; and this is so far borne out by practice, that the coach-masters have found it to be their interest to make the tires of all the fast coaches very narrow. Some of those coaches which travel very fast have the tires not more on the bearing than l£ inch, whilst the heavy or slow coaches have tires of 2\ inches. The mails have tires of 1 inch and £. If a proper set of experiments were made, the breadth of tires would be ascertained for different states of the weather on