|
Horsepower is a term that can be misused. Technically, it is a measure of the rate of doing work. James Watt, the steam engine guy back in the 1700s, established a definition of one horsepower being the rate of work done (comfortably) by one horse, and that was the ability to pull a load that required a force of 180 LB at a speed of about 181 feet per minute (a little over two miles per hour). Although you usually think about horses pulling in a straight line, such as with plowing, horses also created torque by walking in circles pulling on the arms of a horse wheel, but the method of measuring that power, straight line or circular, was the same - force x distance divided by time. Anyway, the Nebraska Tractor Test Laboratory measured horsepower of tractors from the drawbar and horsepower from the belt (or PTO) during their testing. But what they measured from the drawbar dynamometer or the belt-driven dyno was only accurate for the exact air temperature and barometric pressure when the test was made. Doing the same dyno tests on a hot day or at much higher elevatioons would result in lower HP readings. So those test measurements were then corrected to standard conditions of 60 degrees Fahrenheit and sea level barometric pressure. The Nebraska tests also determined what was defined as rated horsepower which was 75% of the maximum corrected drawbar horsepower and 85% of the maximum corrected belt horsepower. This was done to account for other variables and to allow a certain amount of leeway for variable working conditions. Those horsepower ratings were determined throughout most of the two-cylinder era. But some ratings you see are of engine horsepower (such as with garden tractors and lawn mowers) and don't allow for geartrain and other losses, so one really needs to know what the manufacturer's definition of horsepower means. A few years ago, Shop-Vac (and maybe others) got into trouble by advertising their vacuums with what they called Peak Horsepower ratings, each trying to claim a higher value than their competitor. But it was all a bunch of advertising hooey dreamed up by the marketing geniuses. Shop-Vac indicated they could produce 6.5 Peak Horsepower on a 120 volt vacuum. Really? A single-phase electric motor would require an absolute minimum of 40.5 amps at 120 volts to develop 6.5 HP. Kinda hard to get that much amperage out of a 15 amp outlet. So when people talk about horsepower, they really need to be specific about what they are describing.
|
