Drawbar HP

flyingace · Jan 3, 2012

I understand engine or PTO HP measured as some multiplier of torque X RPM. How do they derive this measurement at a drawbar?

buickanddeere · Jan 3, 2012

(quoted from post at 12:58:40 01/03/12) I understand engine or PTO HP measured as some multiplier of torque X RPM. How do they derive this measurement at a drawbar?

Same way.force over distance during a known period of time.

glennster · Jan 3, 2012

here is a link to smoke stack regarding a discussion on measuring drawbar horsepower. pretty interesting
poke here

flyingace · Jan 3, 2012

I found what I wanted to know. The drawbar HP is actually measured using a mechanical device pulled behind the tractor or train. For an engine, the HP is measured using a formula based on torque and RPM. Thinking about it, drawbar HP would seem to be a much more accurate picture of a tractor's power than engine HP.

Ken Macfarlane · Jan 3, 2012

Just force and time, but its limited by the traction of the tractor
which is why high hp light tractors have low drawbar hp.

The peak drawbar pull will let you know how big an implement you
can roughly start moving. Ie just because you have 100 drawbar
hp, doesn't make you equal to another 100 drawbar hp tractor as it
might be at a higher speed lower pull.

Jerry/MT · Jan 3, 2012

It"s the drawbar force (~lbs) X the speed(~ft/sec)/550(~ ft-lbs/sec/hp). You can measure the drawbar force with a load cell and there"s several ways to measure the speed.

Gold-Leaf-Deere · Jan 3, 2012

The story that I think is true is that the drawbar horsepower years ago was based on how many farm horses could pull the load equal to the tractors pulling ability. As a example, by Grandson's 30-60 Aultman Taylor tractor could pull a load equal the load that was pulled by 30 horses.

Indiana Ken · Jan 3, 2012

(quoted from post at 09:58:40 01/03/12) I understand engine or PTO HP measured as some multiplier of torque X RPM. How do they derive this measurement at a drawbar?

By definition: Horse Power is force times distance per unit time, the equation is; 1 HP=33,000Ft-Lb/Min. Typically, the test books will show a horse attached to a rope which goes around a pulley and is then attached to a weight. Since the weight is lifted vertically it is the force used in the equation, the distance must also be measured and the amount of time it took to lift the weight. For drawbar horse power one needs a pull scale to measure the force (pull) and then the speed (distance/unit time) is measured.

For example, if a tractor generates a drawbar pull of 150 Lb and is able to maintain a steady 2.5 MPH, the HP is calculated as follows; Note 2.5 MPH = 220 Ft/Min, therefore we have 150 Lb x 220 Ft/Min = 33,000 Ft-Lb/Min which is equal to 1 HP.

Note - in the above example the tractor may have been pulling a 1000 Lbs of weight to generate the drawbar pull of 150 Lbs - since the weight is pulled horizontally it is the draw pull not the actual weight we use in the calculation.

How does this relate to horses? It has been claimed a horse can walk 2.5 MPH while lifting a 150 Lb weight vertically.

flying belgian · Jan 3, 2012

Not necessarily. For pulling the stalk chopper I want all the pto horse power I can get. Don't need the draw bar pull.

Drawbar HP

flyingace

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buickanddeere

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glennster

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flyingace

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Ken Macfarlane

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Jerry/MT

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Gold-Leaf-Deere

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Indiana Ken

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flying belgian

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