Posted by LenNH on November 29, 2012 at 17:06:34 from (220.127.116.11):
In Reply to: Speed Plowing. posted by High Octane on November 06, 2012 at 13:17:12:
A while back, I sent a note about an old test of plowing speeds (back in the 1920s, I think). The tests showed that horsepower requirements went up drastically as speeds increased, something like the way air resistence goes up with speed (as I remember, for air resistence, the change is "as the square of the speed." This means that if you double the speed, 2 squared gives 4, so air resistence at 60 mph is not twice as high but four times as high as at 30 mph). I don't have any formulas for changes in plow resistence, but I do remember that it was substantial. This is, I suspect, why our steel-wheeled 10-20, which would pull 2-14" plows through thick and thin in second gear, at around 3 mph, would not pull this load at all in third (a bit over 4 mph). My understanding is that tractors back "in the old days" were designed to pull their "rated load" at what was then called "plowing speed." I imagine that 3 mph was considered an economical speed in those days, since the engineers knew that a lot more power would be required to pull those plows at 4 mph, especially on steel wheels, which robbed something around 35% of engine power (this helps explain why tractors were rated 10-20, 15-30 and so on--all that engine power was available on the belt, but a lot less of it went to the wheels). I believe horse plowing speed was nearer 2 mph, so 3 probably felt fast in the 1920s and 1930s. I plowed with a steel-wheeled 10-20 for a good 10 years, and I can personally testify that 3 mph on steel is about the upper limit for your backside. On a gravel road, you couldn't even stand 3 mph--we always throttled back in second or third to get maybe 2 mph on the road. I probably have the plowing report around here somewhere amongst all the useless memorabilia, and I will look and then post anything I find. If you like data and theoretical stuff, you'll find this interesting. It would be very interesting to see what modern plows require in the way of horsepower. They might quite a bit different from the old stuff (our plows were made in the 1920s). Any ag engineers out there who would like to give us an update on this? I'd love to know!
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