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 04-18-2001, 17:09 Post: 26866
dsg

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 Drawbar HP

How do I determine the Drawbar HP. I have a JD 4700 Hst. 48 engine and 40 pto Hp. Thanks, David.






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 04-18-2001, 17:33 Post: 26869
Anthony M. Parente



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David,
The JD technical manual does not specify the drawbar HP. However, since the JD4700 is a CAT 1 tractor, the maximum possible drawbar HP is 45. I hope this helps.
Tony






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 04-18-2001, 18:49 Post: 26877
RickB.



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 Drawbar HP

Drawbar hp info is most commonly developed as part of a Nebraska Tractor test,which as far as I know, is not required of compacts to be offered for sale in Nebraska as it is for larger farm tractors. PTO hp is more easily measured, especially at the dealership level. Another reason for manufacturers not to advertise drawbar HP is it would point out the gross inefficiency of hydrostatic transmissions as compared to a gear drive. As an example, the IH 1066 was offered as a gear drive tractor developing a maximum 100.5 drawbar HP. The hydro version produced 84.88hp. The relative PTO HP were 116 and 113, respectively. All other factors are equal or very close between the two versions of this '70s farm tractor. Info from Nebraske tests # 1081 and 1083, 1971. I doubt your 4700 develops over 30 drawbar hp, but that is only a guess.






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 04-18-2001, 19:45 Post: 26885
Anthony M. Parente



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David,
Rick is right on! I calculated the drawbar HP based on the Nebraska tests for gear Vs. HST transmission, (only 76% effeciency)= 29.26 HP.
The real use of drawbar HP is to maximize farm production which envolves tractor speed, load and fuel consumption.
I chose the HST because I use the loader alot.
What are your concerns about drawbar hp?
Tony






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 04-18-2001, 20:42 Post: 26890
Roger L.



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 Drawbar HP

I agree with Rick and Anthony. As long as there is enough torque available at the rear tire to break traction, drawbar horsepower isn't really very important....and is darned hard to figure. PTO horsepower is probably more useful.






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 04-18-2001, 22:59 Post: 26901
JeffM



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Anthony and Roger, this thread started because of the thread "Plow or?" in which drawbar hp was discussed as a means to determine how many plowshares a tractor can handle. In that regard, drawbar hp is much more useful than gross engine or PTO hp because it is more indicative of the work being performed. I don't know the conditions for the Nebraska tests, but I'll bet a NH TC25 gear drive with ag tires (25 hp gross, 21.7 hp PTO, 2474 pounds) has more drawbar hp and therefore plow-pulling ability than a Kubota 2710 HST with turf tires (27 hp gross, 20 hp PTO, 1740 pounds). I'd rather mow the lawn with the 2710, though.






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 04-18-2001, 23:11 Post: 26902
JeffM



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RickB, thanks for the enlightenment on the Nebraska tests. We may not plow much with compacts and therefore the higher drawbar hp losses with a hydrostatic drive are not as relevent compared to the lesser PTO hp losses which predominate uses such as mowers and brush hogs. But there is one situation where I notice the dramatic difference between gear drive and hydrostatic and that is on the road when going up hills, especially with a load. I have not yet been able to do a true apples and apples comparison (for example, a TC33 and a TC33D on the same road with the same tires and load), but my perception driving different machines is that there is a significant difference in performance in this situation between gear drive and hydrostatic..






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 04-19-2001, 08:23 Post: 26920
Anthony M. Parente



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David, et al
I use the manufacturer's MAX HP rating when choosing the best implement for my JD4700 HST compact. The implement HP ratings are based on the tractor's max HP and assume 2 wheel drive. The implement HP rating can be reduced by 20% for 4WD. This info was provided by my JD dealer and the Landpride rep. I have not been disappointed to date. My JD dealer will call the JD factory to find out the actual drawbar HP.
Tony






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 04-19-2001, 10:01 Post: 26922
Bernie Galgoci



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 Drawbar HP

I hope the copyright police don't come looking for me, but I will give the direct quote for a rule of thumb given in a book I have that deals with farm machinery. I'm sure it assumes a gear, not hydrostatic, transmission tractor. Hope this helps.
"Different ways of rating tractor power and variations in the amount of power needed to simply move the tractor itself through different soil conditions make it difficult to size implements to fit tractors or to size tractors to implements. A rather simple system has been devised by Wendell Bowers, Agricultural Engineer, (Oklahoma State University) to estimate drawbar power under varying conditions if the maximum engine or PTO power are known. The factor 0.86 is used throughout the sequence below. The example given is a tractor with a maximum engine power of 86.5 kW [116 hp]."

a = max. engine power, 86.5 kW [116 hp]
b= max. PTO power = 0.86 x (a) = 74.4kW [100 hp]
c = max. drawbar power (concrete) = 0.86 x (b) = 64.0 kW [86 hp]
d = max. drawbar power (firm soil) = 0.86 x (c) = 55.0 kW [74 hp]
e = usable drawbar power (firm soil) = 0.86 x (d) = 47.3 kW [63.6 hp]
f = usable drawbar power (tilled soil) = 0.86 x (e) = 40.7 kW [55 hp]
g = usable drawbar power (soft soil) = 0.86 x (f) = 35 kW [47 hp]






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 04-19-2001, 10:06 Post: 26923
JeffM



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Bernie, this is great stuff! Probably not very useful because of all the hydrostatic transmissions on compacts and variation in tire types, but I still love it! I guess if you give us engineers a formula it makes us happy, even if it doesn't mean squat in our situation. :>) Seriously, thanks for the info!






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Discussion Boards > Active Subjects > Messages as Posted > Tractor Projects Forum

Thread 26866 Filter by Poster:
Anthony M. Parente 5 | Art White 1 | Bernie Galgoci 1 | dsg 2 | JeffM 3 | John Miller, III 3 | RickB. 1 | Roger L. 1 |




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