i6
RECENT LOCOMOTIVES.
Ratio - ^
l
f Fire-box heating surface to totalGrate area to heating surface,
Contents of one steam cylinder in cubic feet, tothe heating surface in square feet -Length of smoke-box, -
Diameter of chimney, -
Total wheel-base, ------
Engine wheel-base, -
Tender truck wheel-base, -----Driving-wheel base, -----
Distance between the centre of the truck axle and the centreof the first driving-axle, -Distance between centre of back driving-axle and centre ofthe tender truck, - -
Weight of locomotive empty, -
Weight of locomotive loaded, -
Weight on driving-wheels, -----Weight on pony truck, -----
Weight on tender truck, -
Capacity of water-tank, -----
The tractive force per each pound of effective steamsquare inch on the pistons is
= 8 6. 4 l bs .
33-75
The fuel used is bituminous coal.
9.89.
58.1.
428.8.36 in.12 in.31 ft. 1 in.16 ft. 1 y 2 in.6 ft. o in.9 ft - 3 in.
6 ft. io)4 in.
11 ft. n)4 in.57,000 lbs.
74.200 lbs.
40.200 lbs.’8,000 lbs.26,000 lbs.i,3°o gals.
pressure per
Figs. 83 to 95.
The engravings, figs. 83 to 95, represent different patterns of locomo-tives built on the plan which was patented by M. N. Forney in 1866. The
WISM
W
“AMERICAN" LOCOMOTIVE.
^ - - 1 -
h r a IT
PLAN OF "AMERICAN” LOCOMOTIVE.
advantages claimed for this type of engine were fully set forth in apamphlet isued by him, of which the following is a reprint:
The type of locomotive which is generally used in this country is thatknown as the “ American ” engine, an example of which is represented onthis page, having four driving-wheels, a four-wheeled truck and an eight-wheeled tender. The most common size of engines of this kind weighsabout thirty tons (of 2,000 lbs.), and, with the tender loaded, the weightof the whole is a little over 100,000 lbs., of which 40,000 rests on the driving-wheels, and 60,000 lbs. is on the truck and tender wheels. The object aimedat in designing the locomotives illustrated in the figures referred to abovewas to make a better disposition of the weight,—that is, to carry a larger pro-portion of it on the driving-wheels to produce adhesion,—and at the sametime to retain the advantages, which the American engine undoubtedlyhas, of great steadiness and flexibility, or power of adjusting itself to thecurvature and inequalities of the track. A little elementary explanationwill, perhaps, be needed to make the advantages of the improved form ofengine clear to those who are not experts.
It may be stated, as a general principle, that the capacity of a loco-motive to draw loads depends, first, upon the power which is exerted toturn its driving-wheels, and, second, on the friction or “ adhesion ” ofthese wheels on the track. If this adhesion is greater than the resistence ofthe load to be drawn, the engine and train will be moved by the revolutionof the wheels ; if the resistance is greater than the adhesion, the wheels willslip on the track without moving the locomotive or its train.
As the friction of one body sliding on another is in proportion to theweight of the former, the more weight there is on the driving-wheels the
greater will be their friction or adhesion. Therefore, a locomotive similar tothe four-wheeled switching locomotive shown on the next page, having all itsweight on the driving-wheels, is in this respect the most efficient form ofengine, and will draw heavier loads in proportion to its weight than anyother kind, excepting that class of “tank engines” which carry theirsupply of water and fuel on the driving-wheels.
It would seem, then, that in order to build locomotives with greatercapacity for drawing loads, it would only be necessary to increase the weighton these wheels. Experience has shown, though, that a limit to the loadwhich they can safely or economically bear is soon reached ; ana that if itexceeds a certain amount, it will crush the rails and otherwise injure thetrack. Practically, therefore, to increase the capacity of a locomotive toexert its power, it is necessary not only to increase its weight, but also thenumber of driving-wheels, after the load which they carry reaches a cer-tain limit, and therefore two or more pairs of such wheels are generallyused.
As the pistons are connected to one pair of wheels only, in order thatthe others may be rotated by the power exerted on the first pair, and theadhesion of all of them be utilized and assist in drawing loads, they mustall be connected by rods and cranks so as to revolve together. The crank-pins must then, necessarily, be always exactly the same ’istance apart, andthe axles be parallel to each other at all times. But in order that a pair ofwheels may roll easily in a curved path, the centre line of the axle to whichthey are attached must, then, assume a position radial to the curve,otherwise the wheels will roll in a path more or less divergent from thatof the curve, according as the position of the axle departs from that ofthe radii, and therefore the flanges of the wheels on each side of thecurve will come in contact with the rails at an angle, and the abrasion ofboth the flanges and the rails will be in proportion to the inclination of theone to the other. If two or more pairs of wheels are connected togetherby cranks and rods, and the axles are, consequently, attached to a frameand held rigidly parallel to each other, and the wheels are rolled on acurved track, it is obvious that all the axles, being parallel, cannot con-form to the radii of the curve. Thegreater the distance apart of the axles,the more will be their divergence fromthe radii, and the greater the inclinationof the wheels to the rails.* Conse-quently, if the wheel-base of a locomo-tive is lengthened, by placing the driv-ing-axles far apart, the injury to therails on curves by the abrasion of theflanges of the wheels, and the dangerof running off the track, will be in-creased. If the axles are placed neartogether, the wheel-base will be short,and at high speeds, or on a roughroad, the motion will be inconveniently
* This can easily be demonstrated mathematically. Suppose m n and m n , in the dia-gram herewith, to be a curved track, and go a radius of the curve, and a b and c d twopairs of wheels and axles—the latter parallel to, and equidistant from, the radius g 0. Now.in order that the wheels a and c may run on the same right line or track, they must be in the.same plane to which the axles would be perpendicular. If, therefore, from a , the point ofcontact of the wheel with the track, a line, a c , be drawn perpendicular to a b , this line willbe in the plane of the two wheels, and be perpendicular to their axles and to g 0. From 0and c draw the radii a o and c o, and through a draw a line h e, tangent to the curve m n, at a.therefore perpendicular to the radius a 0. Now, as the circumference of a circle is perpendicularto its own radii at the point where they intersect, therefore the tangent h e and the curve mustcoincide at the point a, and therefore the angle which the line a c, lying in the plane of thew^eel, makes with the tangent h e, must be the same angle that the wheel a makes with
the curved track at that point.
In the triangle a f 0 theangle a f o is a right angle ;therefore the angle 0 a f+ f o a = a right angle. Butas the two angles 0 a f +f a e = o a e, which is alsoa right angle, therefore f a cmust be equal to the centralangle f 0 a. This is meas-ured by the arc a g, which isone-half the arc subtended bythe chord ac, which equals thedistance between the axles Itherefore, the angle at whichthe wheels attached to tw»parallel axles will stand tothe rails of a curved track isequal to that which is meas-ured by half the arc of thetrack subtended by a clientequal to the distance betweenthe axles, or the wheel-base,as this distance is called. Thelonger the distance betweenthe axles, therefore, thegreater will be the angle of thewheel to the rail.