Re: Re: Re: on various measurements of horsepower
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Posted by john d. on September 01, 1998 at 06:31:17:
In Reply to: Re: Re: on various measurements of horsepower posted by Kelly See on August 31, 1998 at 15:38:29:
: : : 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. : If it is the case that the Drawbar HP will always be lower than : the PTO rating because of the physical reasons you mention, then does there : appear to be some observed relationship? For instance, drawbar hp : tends to be approximately X percent of max PTO. : Thanks, : Kelly I suppose if you have enough data, you could determine a value for "X" but it would likely be only approximate when applied to an individual tractor. Some tractors are simply more effecient than others at getting the power to the ground. Factors such as tire diameter, radial vs. bias-ply tires, and weight distribution will always play a role. The drawbar hp will even be influenced by using the optimum gear ratio for specific conditions. What you're looking for is a little like trying to predict the on-field performance of two football linemen based upon data gathered in the weight room.
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