HORSE POWER
By Walter R. Arndt
East Main Street, Noel, Mo. 64854
What is the true meaning or value of horse power relative to a steam engine or tractor?
According to Lionel S. Marks Mechanical Engineers Handbook, the power to lift a 550 pound weight one foot in one second or a 33,000 pound weight one foot in one minute, is defined as one "horse power".
The term "one horse power" on a sweep horse-power, means for one horse to pull 165 pounds at a rate of 200 feet per minute. And "twelve horse power" is defined as twelve horses pulling 1980 pounds at the same rate of 200 feet per minute.
According to the Ohio State University test chart covering the July-August 1919 tractor testing, showed the 54 tractors having a factory horse power draw-bar rating, totaled 652.00 horse power. The Ohio State tests gave these same tractors a total of 651.48 Horse power. Or 148.92 pounds pull per tested horse power at a 2.40 miles per hour rate. This converted to 200 feet per minute equals 154.69 pounds pull per tested draw-bar horse power.
In the early days, twelve horses on a six sweep horse-power had sufficient power to operate a thresher with a 24, 26 or 28 inch cylinder and a 44, 48 or 48 inch rear. And in some cases even as large as a 30 x 50 thresher. Or a 24 x 44 thresher with a feeder and grain elevator with bagging attachment. These same threshers required a 12 H.P. steam traction engine. The 10 H.P. steam traction engine, unless in perfect condition, did not have sufficient power in tough conditions as usually found in the bottom 0of stacks or in damp conditions.
Courtesy of Western Canadian Pioneer Museum, Wetaskiwin, Alberta, Canada This is a 1904 Cadillac, 1 cylinder.
Courtesy of Western, Canadian Pioneer Museum, Wetaskiwin, Alberta, Canada Here is a picture of a 1915 Sawyer Massey, 40 HP.
1910 or 1911, if I remember correctly, was the beginning of the double rating for a steam traction engine. The new rating for a 12 H.P. steam traction engine was changed to 12-36 H.P. The 36 was referred to as the actual or brake H.P. And the 12 H.P. was referred to as draw-bar H.P. There-fore can we assume, with the double rating, that 24 H.P. was consumed to propell the engine in traction, leaving only 12 H.P. for draw-bar pull?
We all know that no 12-36 horse power steam traction engine has ever been built that would equal the power of 36 horses on an 18 sweep horsepower. If so, it would be necessary for the engine to pull 36 times 165 or 5940 pounds pull at the rate of 200 feet per minute to equal the belt or rotating power of 36 living four legged horses. Therefore, the 36 H.P. rating should be called or defined by some other name for the units of energy.
Courtesy of Western Canadian Pioneer Museum, Wetaskiwin, Alberta, Canada This is a 1902 American Abell, 15 HP.
Courtesy of Western. Canadian Pioneer Museum, Wetaskiwin, Alberta, Canada Here is a picture of an 1890 Pitts, 10 HP.
NOT actual horse power.
The first, simple and most commonly used method for figuring the horse power of a steam traction engine with the single rating was P x L x A x N over 3 x 33,000 equaled horse power. With the coming of the double rating this method was changed to PxLxAxN = H.P.
33,000
P-Pounds steam pressure
L-length of stroke in feet
A-Area of cylinder in square inches
N-Number of revolutions per minute
There are many other methods for computing the horse power of steam engines. Some are more accurate, but also more complicated. Their computations are based on the gain or loss in the type of valve, type of valve gear, the type of ports, the loss in the steam pressure from the boiler to the cylinder, the back pressure from the cylinder to the exhaust nozzle, the timing or length of the power stroke, the length of the connecting rod and many other items of importance that can increase or decrease the power of an engine.
Due to the extremely high actual or brake horse power rating on a steam traction engine, I would like to see twelve horses on a six sweep horsepower belted to a Prony brake, to see what kind of a rating they would receive. Does anyone have a horsepower so this test could be made? This would be in comparison to a 12-36 horse power steam engine.