Steam engine hitched to gang plow with dynamometer between draw-bar and plow. Dynamometer registering between draw-bar and plow. Dynamometer registering 5000 lbs.
106 South Elm St., Newkirk, Okla. 74647
A good horse hitched to a plow or to a lever of a horse-power can exert a pull of 165 pounds and walk at the rate of 200 feet per minute. He can pull much more than this for a short time, but we are talking about the power that an average horse can maintain all day. This must not be confused with the load that might be hauled on a wagon. We mean the load that can actually be lifted or shown on a dynamometer connected between the horse and the load.
When power machinery came into a couple of hundred years ago or more, engineers and mathematicians adopted the 'foot-pound' as the unit of energy. It is defined as energy enough to lift one pound at the rate of, one foot in one minute. The steam engine came into use at about the same time and it came to be rated according to the number of horses it could equal. Since the engineers had already learned that a horse could put out thirty-three thousand foot-pounds continuously, they called this a 'horse-power and defined it as power enough to lift thirty-three-thousand pounds at the rate of one foot per minute or conversely, power enough to lift one pound thirty-three-thousand feet per minute.
This definition is a bit confusing as 33,000 pounds is an awfully heavy weight and one foot per minute is a very slow speed. A horse would need to be hitched to the end of a lever 200 feet long with the hitch point one foot from the fulcrum to be able to lift that much weight but the horse could walk at the rate of 200 feet per minute and the pull at the end of the lever would be 165 pounds. The problem can be stated: Force: 165 lbs. multiplied by: Speed: 200 feet per minute: Equals 33,000 foot pounds which is one Horsepower. To figure it another way: You take a larger but slower horse could be hitched at a point on the lever 165 feet from the fulcrum where he would have to exert a pull of 200 lbs. and walk at the rate of 165 feet per minute to lift 33,000 lbs. at the rate of one foot per minute. If you were plowing, a fairly fast medium weight team pulls a 12 inch plow 200 feet per minute. A heavier team could pull a 14 inch, but if they walked at the rate of 165 feet per minute you will get about the amount of ground plowed. To sum up, I am trying to say Force multiplied by Speed equals Energy.
The 'drawbar horsepower' of Steam traction engines is tested by connecting a dynamometer between the engine or other load to register the pull in pounds so that it can be multiplied by the speed. Most steam tractors were geared to travel about 2 miles per hour which is very close to 200 feet per minute, so this is a handy figure to use.
A fairly large steam engine on ground soft enough to plow can exert an average pull of 5,000 lbs. on the draw-bar and travel 200 feet per minute. So 5,000 x 200 = 1,000,000 foot-pounds. This divided by: 33,000 equals 30.3 horsepower. A Steam Engine Indicator attached to the cylinder of this engine would show it to be developing about 60 HP in the cylinder. Now what became of half our power? One of the unpleasant facts of life is loss. It begins friction between piston rings and cylinder walls, crosshead and guides, connecting rod bearings, crankshaft bearings, and the valve gear and slide valve can use a lot of power if not well lubricated. The transmission gearing and axle bearings take power but the greatest loss occurs at the contact of the wheels on ground soft enough to plow. To demonstrate; take an engine which we assume to be in good operating condition, hitch it to one of equal size fully loaded with fuel and water but with the steam shut off. You will find that you can pull it very easily on a hard level road. Now engage the clutch so that you have the full friction load of both engines and you will notice that it pulls harder, but on hard level ground you can go easily. Now pull off the road into soft plow land and you will find that you will have all that you go with. This goes to prove that it takes fuly one half of the power of a heavy steel wheeled traction engine to move itself on ground soft enough to plow. Few of the early manufacturers gave any draw-bar ratings for their engines. One leading steam engine builder says in their 1918 catalogue: - 'Our engines will develop from 50% to 75% of their brake HP. on the draw-bar.' Of course the power you can get on the draw-bar varies greatly. On a tightly packed clay and gravel road an engine might put 80% of its power on pulling a string of wagons, but in sand or mud could not even move itself.
When gas and oil tractors first came into use their weight and road speed were about the same as that of the steam tractors of equal power, but they were rated in a different way. About all the early manufacturers gave such ratings as; 10-20, 15-30, 20-40 to their tractor. This meant that when the motor was developing 40 horsepower on the crankshaft you could get about 20 horsepower on the drawbar under average working conditions.
Improvements such as caterpillar treads, rubber tires, and increased power in relation to weight, enable the modern machines to put a much larger percentage of their power on the draw-bar, so we never see such as 20-40 ratings any more.
During most of the time that steam engines were used on the farm the power ratings were somewhat confusing and meaningless. In a 1907 catalogue one manufacturer offered an engine with a 7 x 10 inch cylinder that they called a 9 horse, up to one with a 12 x 12 inch that they called 32 horse. However, they modestly stated in fine print that all their engines would develop three times their rated power. In a 1910 catalogue, another company showed a big double tandem compound that weighed at least 40,000 lbs. with the boiler empty, that they called the 'big forty'. They too admitted somewhere in their literature that their engines might pull three times their rated power. At about that time I remember reading an article by a well known engineer who said that those ratings were a sort of holdover from the early days of steam when the boilers could only carry about 60 lbs. pressure and the speed was lower. A 9 x 12 steam engine running 200 rpm will indicate about 23 Horsepower with 60 lbs. steam at the throttle. It would pull about 20 H.P. on a Prony brake. The brake power will be about 10% less than the indicated, due to friction in the engine itself and the belt and brake bearings. The same engine with 150 lbs. steam and running 250 rpm would show about three times as much power.
Large stationary engines were rated more accurately, usually by stating the horse-power they would 'indicate' at a given speed and steam pressure. The steam engine indicator was used in designing and testing the larger engines, since in addition to showing the power, it also shows exactly how the steam is acting in an engine. It is very difficult to set the valves on a Corliss without an indicator and you need it to set the valve on an 'Automatic'. The steam engine indicator is easy to understand and use. They say that James Watt invented it. The indicator diagram tells the engineer the same kind of story that a car diagram tells your doctor.
All the arguments about ratings and whose engine can pull the most can be settled by a very simple device called the Prony Brake. It was invented about 150 years ago by a French scientist and mathematician named Prony, and is still used even in testing rooms of such people as General Electric and General Motors. Several of the steam engine shows have Prony brakes in operation and most steam buffs find it very interesting to watch them. The way the brake works is very easy to understand and only 8th grade arithmetic is required in the calculation.
All in all the steam traction engine was a wonderfully useful and dependable piece of machinery. It could and did stand an awful lot of abuse. Bad water, poor fuel and rough treatment could slow it down, but it hardly ever quit completely.
The horse would be pulling 165 lbs. plus the friction of the pulleys and rope. During the time that steam engines and horses were used on the farms a rig something like this was often seen. There were usually more lead pulleys and a trolley that carried the hay into the barn. The friction in the pulley bearings and flexing the rope consumed a lot of power. If the load weighed 165 lbs. and ascended at the rate of 200 feet per minute the horse would be putting one horsepower on the load, but he would be pulling much more than 165 lbs. on his end of the rope. Probably about 40% more. In this case he would be developing 1.4 HP during the time the load was being lifted. Since this would only be for about 8 seconds, the overload capacity of a horse would take off the extra pull easily. A well trained horse can develop five times his normal power for a short time.
It's time that 'Yankee ingenuity' gets a rebirth, and our inventors assert themselves.
We say that to all our readers, because we think our readers are full of the kind of ingenuity that made this country great, and led to so many breakthroughs in getting things done.
The rate of growth of foreign patents in the U. S. has more than doubled in the past 14 years, according to IPO (International Property Owners, Inc.), a non-profit group devoted to keeping the patent incentive high.
IPO says that one factor cutting into U. S. patent development is a general attitude against technology and growth, which is even evidenced in some U. S. corporations.
If you are as ingenious as we think you are, you will work on new inventions, and have them patented. When you do, tell us so we can tell everyone else in the Stemgas Family.
Gerald S. Lestz