Re: on various measurements of horsepower
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Posted by john d. on August 31, 1998 at 15:22:39:
In Reply to: on various measurements of horsepower posted by Kelly See on August 31, 1998 at 13:31:10:
: I realize there are different types of horsepower
: calculations, and I have not always been able to
: obtain the same measures of horsepower. But if I
: want to treat two tractors as equal, is there an adjustment
: I can perform on one of the horsepowers (drawbar or
: PTO) in order to make them comparable? With that
: I mean, is there an empirical mathematical relationship between the max PTO horsepower at
: rated engine speed and drawbar horsepower used
: for 10 hour run? Likewise, is there a similar relationship
: between the fuel efficiency (work per gallon during
: PTO test at rated engine speed) and the drawbar fuel
: efficiency (work done per gallon durin 10 hour run at
: 75 percent drawbar load)?
PTO horsepower is measured at the end of the PTO shaft, which is generally connected to the engine by means of a simple gear train. This provides a reasonably efficient means of getting power from one point to the other, and friction losses are usually at a minimum. PTO HP is very close to what would be measured at the engine flywheel. Drawbar horsepower is a different critter. What a tractor will actually pull at the drawbar is a combination of factors, including engine horsepower and traction. It is NOT a figured from PTO horsepower by applying some mathematical constant. Traction depends upon weight, tire-to-pulling-surface adhesion, and the overall balance of the tractor. Balance is achieved through drawbar positioning and weight distribution. The more nearly the Drawbar HP matches the PTO HP, the more efficient the overall pulling setup of the tractor, but it will never reach the PTO HP rating. Friction losses in the drive train and tire slippage will always lower the Drawbar HP compared to the PTO rating. Fuel efficiency tests suffer from the same comparison difficulties.
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