Drawbar pulling question

[plowhog]

If you are worried about lifting the front end, connect the chain to the front and pull backwards.

I'm no expert, but I've read elsewhere it is strongly advised not to do this.

 

[jaxs]

I'm no expert, but I've read elsewhere it is strongly advised not to do this.

Me neither but it doesn't require an expert to know if mfgr didn't provide a dedicated attachment point,they didn't design axles and steering components for dragging things. I attended an auction at a state prison where inmates farmed. The tractors had been busted,broke and welded in places I'm not sure I could cause if I tried.

 

[MHarryE]

Watch tractor pulls illustrates having the attachment point below the axle does not keep the front from coming up. As someone else stated, the pivot point is the tire to ground contact point. Pulling tractors have often have their front end raise, and because the drawbar attaching point is well behind the ground contact point, when the front end raises, the drawbar attaching point lowers until reaching an equilibrium. Sum of the moments must equal zero. If tires get a super bite, there is a very large moment trying to raise the front. As seen in many videos, releasing the clutch immediately reverses the moment diagram and the front end comes down with full weight of the engine(s) in front of the ground contact point providing the wallop breaking tires off, axles off, and even splitting tractors. Operators illustrating the same phenomena are those chaining trees to the rear axle. In those cases torque might be enough to flip the tractor.

 

[etpm]

Thanks folks for all the replies. As JIMS1025R pointed out there might be a peeling force if I pull on the drawbar with the pull point ahead of the rear axle. I did a couple CAD drawings to scale to look at the actual angles, pulling from in front of and behind of the rear axle centerline. Just to see what the forces look like. Because the angle is so shallow both ways I'm not really worried about peeling the drawbar off. I don't think I can get enough traction for that. Still, what I gonna do is pull from directly beneath the rear axle centerline. I'm gonna use a shackle so that it will be easy to chain up to.
Thanks Again,
Eric

 

[Egon]

You are switching from a drawbar in tension to a drawbar in compression. Completely different compilation of forces that the original design was intended for.

 

[tjandrews]

Reading in another thread about rollovers, and recalling how I almost rolled my 9N over backwards shortly after I bought it made me think some about pulling with my Yanmar YM2310.
When I almost rolled that old Ford over backwards it was because of the way I was pulling and because it was my first tractor. I have learned a lot since then. So, now I'm driving a lighter tractor with more horsepower. It will soon have 320 pounds of wheel weights added. I suspect that the added traction may be a problem when pulling logs if I'm not careful.

The previous owner of our IH 424 had problems with the front end raising when towing heavy loads uphill. He welded together a box, attached it to the front end, (There are points on that front end designed for mounting stuff) and filled it with firebrick. Problem solved.
We left it on there for added stability when carrying 3-point implements. The blade you see here is light and wouldn't be a problem, but put a 60-gallon sprayer on there, fill it with water, and try spraying up a hill, and it can be a different story.

 

[Little Red Tractor]

If your point of pull is above the line of your rear axle, you're essentially driving out from under the tension of whatever you're trying to pull. That will flip it. Did it a long time ago with a 7 HP Beaver garden tractor--have the scar to prove it, I'd rather still have that little Beaver tractor.

 

[etpm]

You are switching from a drawbar in tension to a drawbar in compression. Completely different compilation of forces that the original design was intended for.

Whether pulling or pushing on the drawbar the bolts holding it to the tractor will see the same load. The drawbar on my tractor is so large in diameter that my tractor cannot develop enough force to bend it. It is surprisingly, to me, beefy.
Eric

 

[RancherGuy]

... Still, what I gonna do is pull from directly beneath the rear axle centerline. I'm gonna use a shackle so that it will be easy to chain up to.

If you are concerned about the front end coming up, your idea is not recommended. In physics, (statics, actually), it is not where the point is horizontally, it is where the pull point is vertically that creates the torque to lift the front. As SmallChange stated, the torque is relative to the point where the tires contact the ground; has nothing to do with the axle. This means the lower the connection point is to the ground, the lower the lifting torque.

What is possible, is to control how high the front wheels lift if indeed they lift at all. MHarryE's description of tractor pulls mentions this point. If a 'pull' tractor were to pull from their axle and not from a bar that extends well behind the axle, every one of them would flip. The key is to use a solid drawbar that extends the pull point behind the tire contact point. When the front end comes up, this pull point drops down. As it drops, the connection point is lowered and the torque is reduced (see paragraph above). The further away/behind from the tire (ground) contact point, the lower the front tires will be able to rise.

 

[etpm]

If you are concerned about the front end coming up, your idea is not recommended. In physics, (statics, actually), it is not where the point is horizontally, it is where the pull point is vertically that creates the torque to lift the front. As SmallChange stated, the torque is relative to the point where the tires contact the ground; has nothing to do with the axle. This means the lower the connection point is to the ground, the lower the lifting torque.

What is possible, is to control how high the front wheels lift if indeed they lift at all. MHarryE's description of tractor pulls mentions this point. If a 'pull' tractor were to pull from their axle and not from a bar that extends well behind the axle, every one of them would flip. The key is to use a solid drawbar that extends the pull point behind the tire contact point. When the front end comes up, this pull point drops down. As it drops, the connection point is lowered and the torque is reduced (see paragraph above). The further away/behind from the tire (ground) contact point, the lower the front tires will be able to rise.

I have 3 choices from where to pull. I can use the point where the top link attaches, the arms of the 3 point hitch, or the drawbar. The top link is too high. The 3 PH arms can be positioned where ever I want and they are well behind the axle centerline. So if too high they would tend to torque the front end up. But even if set low to the ground will they tend to raise the front end? I need to think about this a little. Using my Ford 9N I nearly flipped it over pulling a big log. Using a drawbar in the 3 PH arms. Scared the crap out of me. I was truly surprised that the front end didn't break when it came crashing down. Lucky for me that the tractor torqued to the right and came down on a bunch of blackberry bushes which lessened the iimpact. Well, I now have to add 3 more points to the previous two mentioned. Using the drawbar, which is below the rear axle, the chain can be connected behind and below, on the centerline and below, or ahead and below. These options need to be compared to the 3PH arms option of much farther behind and a varying degree of below. Time to make some more drawings.
Eric