Effective horsepower is the power converted to useful work. In the case of a vehicle this is the power actually turned into forward motion on a chassis dynamometer. In its cleanest form, it's also called "True HP" - the amount of power transferred to the drive roller plus the dyne parasitics, corrected the chosen atmospheric "correction factor".
In automobiles and motorcycles, "effective horsepower" is sometimes specified as wheel horsepower. All automotive type chassis dynamometers measure "True HP". Some companies then apply various, manufacturer specific produced inflation factors to boost up the displayed horsepower numbers for marketing purposes. It's common for many "mass market" dyno operators to not even be aware that the inflation is added.
Whereupon the problems arise.
As stated above, different companies choose to apply different amounts of power figure inflation to the power actually measured at a chassis dyne's drive roller - ranging from 0% (known as True Horsepower) to as much as 30% or more on common mass market dynamometer systems.
This random amount of power figure manipulation between manufacturers makes it impossible to compare power figures produced on different dyne systems - unless they specify "True HP" which indicates that they have added nothing other than the dyne's own parasitic drag (mostly wind and some bearing friction) and corrected to the test's atmospheric conditions.
"True hp" will be 10% to 20% or more lower than the engine's power "bhp" ratings because of a loss through the drivetrain, especially notably, the tires.
On a chassis dynamometer, "True hp" scale wheel horsepower will be a lower number than other chassis dynamometer variably adjusted upward power figures
History of the term "horsepower"
The term "horsepower" was invented by James Watt to help market his improved steam engine. He had previously agreed to take royalties of one third of the savings in coal from the older Newcomen steam engines.[7] This royalty scheme did not work with customers who did not have existing steam engines but used horses instead. Watt determined that a horse could turn a mill wheel 144 times in an hour (or 2.4 times a minute). The wheel was 12 feet in radius, thus in a minute the horse travelled 2.4 × 2π × 12 feet. Watt judged that the horse could pull with a force of 180 pounds (just assuming that the measurements of mass were equivalent to measurements of force in pounds-force, which were not well-defined units at the time). So:
his was rounded to an even 33,000 ft·lbf/min.[8]
Others recount that Watt determined that a pony could lift an average 220 pounds 100 feet (30 m) per minute over a four-hour working shift. Watt then judged a horse was 50% more powerful than a pony and thus arrived at the 33,000 ft·lbf/min figure.[9]
Engineering in History recounts that John Smeaton initially estimated that a horse could produce 22,916-foot-pounds per minute. John Desaguliers increased that to 27,500-foot-pounds per minute. "Watt found by experiment in 1782 that a 'brewery horse' was able to produce 32,400-foot-pounds per minute". James Watt and Matthew Boulton standardized that figure at 33,000 the next year.[10]
Put into perspective, a healthy human can produce about 1.2hp briefly (see Orders of magnitude (power)) and sustain about 0.1hp indefinitely, and trained athletes can manage up to about 0.3 horsepower for a period of several hours.
Most observers familiar with horses and their capabilities estimate that Watt was either a bit optimistic or intended to underpromise and overdeliver; few horses can maintain that effort for long. Regardless, comparison to a horse proved to be an enduring marketing tool.
Horsepower from a horse
R. D. Stevenson and R. J. Wasserzug published an article in Nature 364, 195-195 (15 July 1993) calculating the upper limit to an animal's power output. The peak power over a few seconds has been measured to be as high as 14.9 Hp. However, for longer periods an average horse produces less than one horsepower.
[edit] Conversion of historical definition to watts
The historical value of 33,000 ft·lbf/min may be converted to the SI unit of watts by using the following conversion of units factors:
* 1 ft = 0.3048 m
* 1 lbf = gn × 1 lb = 9.80665 m/s2 × 1 lb × 0.45359237 kg/lb = 4.44822 kg·m/s2 = 4.44822 N
* 60 seconds = 1 minute
And the watt is defined as
so the historical figure of 33,000 ft·lbf/min converts exactly to the modern definition.
The make up of any "culture" must evolve or die.....
