THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



364 



A FEW OBSERVATIONS ON THE FLY-WHEEL, AND ITS 

 APPLICATION TO THE STEAM ENGINE. 

 Till- admirable collector and distributer of power, is so important 

 1 feature of the steam engine, that too much attention cannot be given 

 to determine the proportion best calculated, to insure a sufficent de- 

 gree of regularity in its motion, to answer general purposes; it is at 

 the same time equally important to avoid all superfluous weight in its 

 rim, because this imperfection not only creates unnecessary expense 

 in tiie construction, but also occasions a portion of the etTectiye power 

 of the engine to be sacrificed, to keep the useless mass in motion. 



In order to obtain the degree of regularity of motion which is in 

 most cases requisite, the energy of the rim of the fly-wheel must be 

 so proportioned to the power exerted by the piston, as to prevent the 

 constantly varying effect of the power of the steam communicated 

 through the crank, from sensibly affecting the regularity of the motion 

 of the fly-wheel. 



The same amount of regularity is not always required, and tre- 

 quently, steam engines are applied to drive machinery of such a de- 

 scription, as will to a certain extent, equalize the irregular action of 

 the steam through the crank ; a corn-mill for instance, requires much 

 less fly-wheel than would be imlispensable for a cotton, or flax mill, 

 because the energy of the mill stones, produces the same kind of 

 effect as is produced by the fly-wheel itself, and in some cases, when 

 flv-wheels are directly attached to the machinery driven, they might 

 be made sufficiently powerful to dispense with the engine fly-wheel 

 altogether, in as far as regularity of motion is concerned ; but if ad- 

 vantage were taken of this circumstance, very great strain would be 

 thrown upon all the mechanism between the crank and the fly-wheel 

 of the machinery driven, which being frequently considerable, would 

 be rapidly destroyed. A fly-wheel may therefore be considered in 

 most cases indispensable in, or very near the engine-room. 



Having had considerable experience in the construction of steam 

 engines, under circumstances which enabled me to establish a regular 

 scale of proportions, between the length of stroke and the relative 

 diameter, speed, and energy of the rim of the flywheel, aud the fol- 

 lowing rules having been put to the test of many trials, I am induced 

 to submit this paper for insertion in the Journal. 



The following table will show the length of stroke, the speed of 

 the piston, the number of double strokes per minute, the diameter, 

 circumference, and speed of the fly-wheel, which I have adopted, and 

 upon which many of the following rules have been established. 

 TABLE A. 



[November, 



The dimensions and weight of the rim of the fly-wheel, may be 

 determined by the following rules; (note— in the calculation of the 

 energy of fly-wheels, the boss and arms are not taken into considera- 

 tion, they should be made as light as prudence will permit.) 



Rule 1. To determine the mean diameter of the fly-wheel, mea- 

 sured in the middle of the breadth of the rim. 



Miilliply the length of stroke of the engine by 3-82, the product mill be 

 the diameter cf the rvheel, measured in the middle of the breadth of the 

 rim. 



The above proportion being adopted, will determine the following 

 relative conditions. 



1st. The rim of the fywheel will run 20 ftet per second, nhen the 

 piston travels 3i feet per second; or in other terms, 



•2nd. The speed of the rim of the fywheel, will be to the speed of the 

 piston as G : 1 ; (note— this is not mathematically correct, because for 

 the mean speed of the piston to be 1, when the speed of the middle 

 of the rim of the fly-wheel is (5, it would be requisite that the half 

 circumference of the fly-wheel should be G, when the radius of the 

 crank is 0-5, in which case the circumference of the fly-wheel being 

 12, the piston for one revolution of the wheel would make a double 

 stroke — 2 feet, or twice the length of stroke, so that when the 

 stroke = 1, the circumference of the wheel should be 12, and its 



diameter necessarily _ ,\,^ = 3-8197, &c., which should be the 



constant multiplier, instead of 3-82 that, with a view of avoiding 

 useless decimals, I have adopted, the difference resulting therefrom 

 being of no practical importance, since the multiplier 3-&2 gives 

 0'OU04 to 1 instead of G to 1.) 



3rd. The circumference in feel of the flymhed, will be equal to the 

 length of stroke of the piston in inches. 



4th. The speed in feet per second of the middle of the rim, will be 

 exactly one tenth of the speed of the piston in feet per minute. 



Area of cross section of the rim of the fywheel. Ten square inches 

 area of cross section of rim, will answer very well when the peri- 

 phery of the rim of the wheel travels at the rate of 10 feet per 

 second, and could be adopted as a constant area for that speed, if the 

 effective load per h. p. on the piston, was a constant load for every 

 engine; this would be the case if the stroke for every power was the 

 same, but the speed increases with the power of the engine, and the 

 load on the piston varies inversely as the speed, so that the above 

 proportion being determined for an effectual load per h. p. of 155 lb. 

 on the piston, when travelling at the rate of 213 feet per minute, 

 which load and speed are those of a 20 horse engine— then the ef- 

 fective load or the speed at which it travels, must be taken into 

 consideration in the calculation, for, with an uniform load and 

 speed as above determined, the section of the rim in square inches 

 per H. P., would be found by multiplying the square of 10 feet per 

 second, or 100 by 10 square inches, and dividing the product by the 

 square of the true velocity of the rim, the cross section of which is 

 to be found, or in more simple terms, by dividing the constant number 

 1000, by the square of the true velocity per second, of the rim, the 

 cross section of which is required. 



But as the load and speed vary with the power of the engine, it 

 will be requisite to multiply the above quotient by 21-3, the standard 

 velocity of the rim in feet per second, and to divide the product by 

 the true speed in feet per second of the rim, the cross section of 

 which is required, the quotient will be its area in square inches- 

 per H. P. 

 Therefore when V = True speed of the rim in feet per second. 

 V- = Square of ditto. 



A =: Area of the cross section of the rim in 

 square inches per H. P., we shall have 



Formula 1. 

 21-3 _ 10- X 10X21-3 



io=xio 



X 



^^^ = A, from which 



V2 

 results, 

 Rule 2. To find the area in square inches per h. p. of the cross 



