Re: Re: Re: Re: What kind of horses are tractor horsepower measured in?
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Posted by Nate on June 19, 1998 at 10:35:46:
In Reply to: Re: Re: Re: What kind of horses are tractor horsepower measured in? posted by Doug Hack on June 16, 1998 at 22:00:24:
: Of course my original question wasn't about horses, or even Horsepower, but about the testing and calculating techniques and comparisons to automobiles. The discussions on torque, rpm and reliability are very relevent. pto horsepower and automobile horsepower are measured the same way. A variable braking device (often a water pump or a generator) is attached to the powered output shaft. On a car this may be the crankshaft or the rear wheel. This braking device is allowed to be free in the direction of rotation (it would spin around if you didn't hold it back). An arm is attached to the braking device with a place to put weights 1 foot from the centerline of the output shaft. Bit by bit the engine is throttled up and weight added to keep the brake from spinning. When the throttle is maxxed the weight hanging on the shaft is noted and this is the ft-lbs of torque at whatever the engine speed happens to be. The load on the brake can then be changed (ie. more or less water supplied to the pump) to vary the engine speed. The weight on the arm is then adjusted for balance and a new torque reading taken. In the case of a tractor there is usually just one speed, (the governed speed). This torque number is then run through the formula HP = Torque x RPM / 5252. This gives the horsepower whatever speed was used for the calculation. Drawbar horsepower is measured by taking the max pull at different speeds (this isn't the weight being pulled it's the tension in the cable) and multipying it by the speed of the tractor in feet per second and diviving by 550. So HP = Pull(lbs) x Speed(fps) / 550. Horse horsepower is measured like drawbar horsepower. Nate
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