Beach Hill Road, New Ashford, Massachusetts 01237
Horses have been with us for about 4,000 years. In the draft horse class, 2- and 4-horse teams were quite common, 6- and 8-horse teams were used on the large freight wagons. We still have the 8-horse Budweiser team. Twenty to 30-horse teams were used to haul the early western combines; a few 40-horse teams, other than 40-horse circus show teams were actually worked. All this is is the pulling power of horses directly applied to moving various size loads.
About 300 years ago horses were used to develop rotary power, first the sweep power, (1 to 16 horses hitched to levers attached to a vertical axle.) Then about 1800 circular and treadmill type horse powers appeared so we had pulley or belt power of from 1 to 16 horsepower. Everyone lived with live horsepower and had a good idea of the power of the horse, then the mechanical horse appeared. Early steam engines replaced horse powers. Steam and gas tractors started to replace horse teams and confusion started.
James Watt developed the horsepower formula so that he could rate the power of his steam engine as compared to the power of a pulling horse or combination of horses. He actually experimented with a draft horse and found, over an average day, a moderately pulling horse could raise 100 lbs. of coal ore out of a mine shaft 220 feet deep and the horse walked the 220 feet needed to raise the load to the surface in one minute. This amounts to 100 x 200 or 22,000 foot pounds of work in one minute. To compensate for friction loss in his engines, Watt added 50% thus 150 x 220 equals 33,000 lbs. of work in one minute and this became the standard 1 HP. This can be broken down in a number of ways lifting 3,300 lbs. 10 feet in one minute; lifting 1,000 lbs. 33 feet in one minute; lifting 550 lbs. 1 foot in one second; lifting 1,980 lbs. or 99 tons 1 foot in one hour. Simplified one horsepower amounts to hauling 150 lbs. of coal out of a hole 220 feet deep in one minute.
In the beginning mechanical horsepower and live horsepower appeared to be distant relatives and to this day many people still think they are not closely related. Watt and other steam engine manufacturers, and later the early steam traction engine and gas tractor manufacturers, knew mechanical horse power and did a good job of promoting this type of horse power. At the same time generations of horse owners and users knew all about live horsepower. Now note the differences using the treadmill type horsepower and the early Fordson as simple examples. A cordwood saw belted to a 1 horsepower would saw wood; a 2 horsepower belted to a small threshing machine would thresh grain so when early small farm type steam engines came on the market the farmer purchased a 1 HP engine to saw wood or a 2 HP engine to pull a threshing machine and they could not handle the job. They found they needed a 3 HP or a 6 HP steam engine to do the previously mentioned same work. The same applied to early gas engines except they needed a 4 HP and an 8 HP gas engine to do the same work as the 1 or 2 horsepowers. Note the differences between live horsepower and mechanical horsepower also between steam horsepower and gas horsepower.
From 1917 to 1922 the Fordson started replacing horses by the thousands. They were often overrated at 10-20 that is 10 HP on the draw bar and 20 HP on the belt. Actually it was about an 8-20. University of Nebraska tractor tests rated it 6 HP on the draw bar and 18 HP on the belt. Let us use this rating. Buyers thought it could draw as much as 6 horses or had the belt power of 18 horses on an 18 horse sweep power, many arguments developed and how wrong they were. A horse properly shod and trained for pulling can actually produce a direct pull equal to his own weight for a short distance. Using the Budweiser team each horse weighs between 2,200 and 2,500 pounds, say 1 ton each or a total of 8 tons. The Fordson weighs about 2,800 pounds and could develop a direct pull of about 50% of its weight. Any two horses of this team could pull the Fordson backwards for a short distance yet the farmers expected it to pull as much as 6 or 8 horses, it could not. However, it could in this manner: the horses had to stop for frequent rests while the old Fordson kept right on going so in the course of a day it did as much, or more work than the 6 to 8 horses; the same for the 8 HP gas engine on the threshing machine. The two horses had to stop and rest, but the old gas engine kept chugging away and produced much more grain. So horsepower can be very misleading, foot pounds of work is more realistic and is widely used, however, other ratings are in the future.
From the previous paragraphs it is obvious some horsepower variations exist. There is the difference noted in steam and gas horsepower. Many think a steam engine has more power than a gas engine and it does appear that way. This is due to several factors: one a different formula is used to rate each one. This will vary as there are several formulas to rate steam and several ways to rate gas; none will show identical results. The original steam manufacturers purposely under rated their engines so that they could compete favorably with horses while the early gas engine manufacturers overrated their engines, so that they could show they had more horsepower in relation to weight than steam. Steam engines had to combine the weight of both boiler and engine producing a high weight to horsepower ratio. The real answer is brake horsepower where the engine is actually tested on a Prony brake; a close reading of the power developed is obtained by turning the torque of the crankshaft into a lever arm that presses on a scale resulting in an actual load applied. To settle all these arguments and to come up with a universal measurement of power, kilowatts in place of horsepower may be the answer. Several large manufacturers are already rating their engines in both horsepower and kilowatts. The auto manufacturers are also considering kilowatts in place of horsepower.
Now 746 kilowatts equal 1 HP. How will one relate it to a simple easily understood comparison when the old horsepower is no longer with us? Engineers and technicians are working on this, perhaps they will come up with an easily understood formula. Presently it looks like horse-power will go the way of candlepower. When electric light bulbs first appeared they were rated in candlepower, now light is rated in lumen show many know what a lumen is, on the other hand why worry this is the push button age?
In closing, when I started this article I thought I knew what I was talking about, now I know differently. I know and can see what candlepower is but still don't know what 1 lumen is. I know what 1 kilowatt is, all I have to do is look at my light bill, but I'm having a problem applying kilowatts to my old engines and tractors.