Horsepower

“ A horsepower is equal to the work of at least ten men, and forty million horsepower would be equal to the work of 400,000,000 men! Why, all the people in the United States today are only 90,000,000, including babies. ”

“ It was established by the great Watt, who determined that the average power exerted by a horse was equal to about 22,000 foot pounds raised per minute; but this was thought by him to be too little, so he increased it by 50 per cent., and so arrived at what is the present horsepower, 33,000 foot pounds raised per minute. Foot pounds bear no relation to our C.G.S. system of units, and it is most desirable that we should have some unit of power, somewhere about the horsepower, to enable us to convert at once watts into horsepower. ”

“ Junior Spaceman Howard Reed knew that away back in the Twentieth Century, the average engineer could make a guess, count on his fingers, and come up with a pretty shrewd estimate of the horsepower per cubic inch that could be stored by the various ways and means available to the age. ”

“ These days the light powerful aeroplane engines we hear roaring over our heads 29 are generating one horsepower of energy for every three or three and a half pounds of dead weight, and engines have been constructed weighing only one pound to every horsepower, though they are impractical for general use. ”

“ To give an illustration, it may be stated that if a man weighing one hundred and sixty-five pounds ascends a flight of steps ten feet high in three seconds, he exerts for the time being just one standard horsepower.
A small balloon which can lift one hundred pounds of lead three hundred and thirty feet high in one minute exerts one-horse power. ”

“ That of course is a gigantic achievement for a month. Every engine has at least 1,200 h.p. If in measurements of horsepower I compare the present with the former World War, then the present achievement is 40 times as great. ”

“ ENGINE TESTS AND BOILER EFFICIENCIES. By J. BUCHETTI. This work fully describes and illustrates the method of testing the power of steam engines, turbines and explosive motors. The properties of steam and the evaporative power of fuels. Combustion of fuel and chimney draft; with formulas explained or practically computed 255 pages, 179 illustrations. $3.00
HORSEPOWER CHART. Shows the horsepower of any stationary engine without calculation. No matter what the cylinder diameter of stroke; the steam pressure or cut off; the revolutions, or whether condensing or non-condensing, it's all there. ”

“ From twelve to sixteen means from twelve to four o’clock.”
“But this H-P, that will wait?”
“H-P must mean automobile. H-P, horsepower, is the way they indicate strength of the motor. A twenty-four H-P is an automobile of twenty-four horsepower.” ”

“ HORSE-POWER. The device, frequently seen in farmyards, by which the power of a horse is utilized to drive threshing or other machinery, is sometimes described as a “horse-power,” but this term usually denotes the unit in which the performance of steam and other engines is expressed, and which is defined as the rate at which work is done when 33,000 ℔ are raised one foot in one minute. ”

“ By calculations as to the mean strength of animals, it appears that a horse drawing horizontally, and at the rate of two miles and a half in an hour, can work for eight hours in succession against a resistance of 200 pounds. If that pace be quadrupled, he finds an eighth part of the time sufficient. Thus we can pretty nearly measure a horse’s power in harness. Whether we are carrying supposed improvement too far, and sacrificing strength and endurance to speed, is a question not difficult to be resolved. ”

“ This conventional horse-power is the unit commonly employed for estimating the power of engines. The horse-power-hour, or the work done by one horse-power in one hour, is nearly 2 million foot-pounds. ”

“ You will be surprised to know that two horses, when doing their easiest work, drawing a loaded car on a perfectly level road, exert from two to three horse power. I have mentioned a car in Philadelphia where we use between two and twelve horse power. A horse is capable of exerting eight horse power for a few minutes, and when a car is being driven up grades, such as I see in Boston, for instance, pulling a load of passengers up these grades, the horses must be exerting from 12 to 16 horse power, mechanical horse power. ”

“ A statement of indicated horse-power supplies a measure of the force acting in the cylinder of an engine, but the power available for doing external work off the crank-shaft is less than this by the amount absorbed in driving the engine itself. ”

“ WHAT AMOUNT OF POWER IS NECESSARY.—In the consideration of any power plant certain calculations must be made to determine what is required. A horse power means the lifting of a certain weight, a definite distance, within a specified time.
If the weight of the vehicle, with its load, are known, and its resistance, or the character of the roadway is understood, it is a comparatively easy matter to calculate just how much power must be exerted to overcome that resistance, and move the vehicle a certain speed. ”

“ Power and Time.—You are thus brought face to face with another thing which is just as important, namely, that, in considering power, time, as well as energy, must be considered. If a man, by superior strength, could be able to raise 550 pounds once within a second, then skip a few seconds, take another hold, and again raise it that distance, he would not be developing one horse power for a minute, but only for one second while he lifted the weight. For the whole minute he would only develop a certain number of foot pounds, and less than 33,000 foot pounds. ”

“ Of their causes and effects.—The horse, like all organized beings, is possessed of a weight and a force peculiar to himself. The weight inherent to the material of which the animal is composed, renders the mass inert, and tends to fix it to the ground. The force, on the contrary, by the faculty it gives him of moving this weight, of dividing it, of transferring it from one of his parts to another, communicates movement to his whole being, determines his equilibrium, speed and direction. ”

“ Now, in harness, the horse has naturally the same two gaits or attitudes, and it is quite true that he can start away with a carriage either in the one or the other; but the means by which he succeeds in this effort—the physical powers which he calls into action, are essentially different:—in the one case he works by his muscles, and in the other by his own dead, or rather living, weight. In order to grind corn, if any man were to erect a steam-engine over a fine, strong, running stream, we should all say to him, ‘Why do you not allow your wheel to be turned by cold water instead of hot? ”

“ HORSE-POWER. A comparative estimate of the capacity of steam-engines, by assuming a certain average effective pressure of steam, and a certain average linear velocity of the piston. The pressure multiplied by the velocity gives the effective force of the engine exerted through a given number of feet per minute; and since the force called a horse-power means 33,000 lbs. acting thus one foot per minute, it follows that the nominal power of the engine will be found by dividing the effective force exerted by the piston, multiplied by the number of feet per minute through which it acts by 33,000. ”

“ The amount of fuel required per horse power per hour, by modern compound engines, is from about 11⁄2 to 3 lbs., and by common condensing engines from 3 to 5 lbs. per horse power per hour.
The unit or measure of a horse power is the amount of power required to lift 33,000 lbs. one foot high in a minute. [62]
[62] See page 407, Vol. II.
Nominal horse power is a term used to represent the commercial rating or power of an engine, and is usually based upon the area of the piston. ”

“ The mark of the old utility of the animal in varied employment is retained in our use of the term horse-power in measuring the energy of engines. That gauge of strength of old determined what man could do in the severest taxes upon the forces at his command. In attaining the point where, owing to the possession of horses, he could use this standard, he won a great way beyond the station of his ancestors, who had but the strength of men at their command. ”

“ It takes a very powerful horse to develop one horse-power for a considerable length of time. It would take a hundred horses to supply the power for even a small airplane, and they would142 weigh a hundred and twenty thousand pounds. An airplane motor of the same power would weigh less than three hundred pounds, which is a quarter of the weight of a single horse. It was this powerful, yet most delicate, machine that we were called upon to turn out by the thousand. ”

“ There are few compound engines, but what, on account of the friction of parts against one another, will require a third part more power to work them when loaded, than what is required to constitute a balance between the power and the weight. ”

“ This speed of thirteen leagues an hour, which blows a horse in a quarter of an hour’s race, the locomotive keeps up and even exceeds as long as may be desired. No comparison, you see, is possible between the iron steed and the steed of flesh and blood.
“Let us turn to the subject of the horse’s strength. [365] A riding horse carries on an average from 100 to 175 kilograms at a slow gait. If the load is a rider of 80 kilograms, the horse can travel seven hours and cover ten leagues of four kilometers each. ”

“ When the farmer hears of an eight horse-power machine he thinks of the wonderful things eight good horses can do on the road, and is surprised when the machine fails to go up hills that teams travel every day; he does not understand it, and wonders where the power comes in. He is not enough of a mechanic to reflect that the eight horse-power is demonstrated in the carrying of a ton over average roads one hundred and fifty miles in ten hours, something eight horses could not possibly do. ”

“ At 60 miles 24 horse power would be necessary—twice that required to carry the same weight at 30 miles an hour. At 120 miles an hour 60 to 75 horse power would probably be necessary, and the weight carried per horse power would be only 10 or 12 pounds. At such high speed the resistance of the operator’s body and the engine is a formidable factor, consuming 64 times as much horse power as at 30 miles an hour. At speeds below 60 miles an hour this resistance is almost negligible. ”

“ To this speed there is a certain limit, at which the whole power of the horse will be necessary to move his own body, and at which, therefore, he is incapable of carrying any load; and, on the other hand, there is a certain load which the horse is barely able to support, but incapable of moving with any useful speed. ”

“ The load which a horse can draw is about fifteen times greater than the power exerted, supposing the road to be hard and level, and the carriage to run with little friction; and the horse, which at starting, can throw into the collar a weight or force equal to two hundred and sixteen pounds, will draw a load of three thousand two hundred. ”

“ In agricultural districts this form of power is still sometimes used to run threshing machines, cider mills, wood-saws, and the like. Another application of horse-power to the same ends is accomplished through harnessing a horse to a long lever like the spoke of a wheel, fastened to an axis, which is made to revolve as the horse walks about it. ”

“ The vast majority of the many millions of horses that are employed every day in helping on the world's work, use their strength without gain or loss through leverage, and with only the aid of rolling friction to increase their capacity as beasts of burden.
To a certain extent horse-power is still used with the aid of the modified treadmill just referred to—consisting essentially of an inclined plane of flexible mechanism made into an endless platform, which the horse causes to revolve as he goes through the movements of walking upon it. ”

“ What powers have we found used in transportation up to a hundred years ago? First there was human power, either walking or plying oars or paddles. This energy is limited; walking is necessarily a slow process, and rowing is seldom a rapid mode of travel. Then came horse power, used first to carry travelers or goods and later to draw carriages and wagons, conveying passengers and freight. Horse power is superior to human power both in speed and in endurance, but it also has its limits and often fails at important times. ”

“ Fig. 66.—Twin-cylinder Two-stroke Engine with Crankchamber Compression.
98
CHAPTER XI
HORSE POWER AND THE INDICATOR DIAGRAM
A book on “The Petrol Engine” would hardly be complete without some reference to horse-power and the indicator diagram. The following definitions must be carefully studied.
Work.—A force is said to do mechanical work when it overcomes a resistance in its own line of action. The line of action of a force is a line indicating the direction in which the force acts. Engineers measure work in foot-pound units. ”

“ In this comparison, the engine is taken at its most advantageous speed, while horse-power is taken at its least advantageous speed, if regard be only had to the total quantity of weight transported to a given distance. ”