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
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.
