Preventing tractor back flip

[SPYDERLK]

All,

I just joined TBN and part of the registration is posting for the first time. This string looked particularly interesting, anyway - what is the moral of the story? What should I know to not kill myself trying to move an object too heavy for my JD 1050? In a previous life, I had bad experiences drawing vectors for a demanding (and obnoxious) instructor - when someone recommends getting out the paper & pencil, I generally look for the door. Is it correct to say that pulling from the front while in reverse is safest?

Jim

On a flat surface, take a piece of plywood, lay it with one edge just a little behind the rear tire ground contacts and lift the other edge til the plywood touches both tires and the drawbar end. Measure the angle wrt the surface. This is the tip angle at which the drive force causing a tip and the load force acting on the end of the fixed drawbar are both acting at ground level. This cancels the tip force. A slow tip will not go further. A fast tip will "coast" higher but at the same time be resisted by load force because the drawbar end will be below ground. A fast tip has a cascading effect because it accelerates the tractor CenterOfMass upward. This acceleration causes greater downforce on the rears, thereby increasing traction. Without wheelslip or engine bog the force geometry says the tip will speed up as you tip - a chain reaction. If your measured angle is 30ｰ you are pretty darn safe because a tractor takes about 60ｰ from level before it will fall over backward - the tip has to be so fast it will coast on up an additional 30ｰ. If its 40ｰ or more I would worry some and try to lengthen or lower the drawbar until it is below 40ｰ.
larry

 

[Short Game]

I admit I'm a guy who is slow to go looking at previous threads on a current subject, what with close to two and a half million posts in the can, but I'm not a great reader (lysdexia). But this thread is less than two weeks old, and I took the two weeks to read most of it in something approaching real time. I have had my say on what can happen pulling backwards from a bucket hook. That cost me $2,000 in parts and a many hours of work once. I still do it, but not so aggressively.

While I never gave the back flip much thought, it seemed that I believed that if your pulling point was lower than the rear axle, it would not happen. This thread made me rethink the problem and that rethinking is what changed my mind. I can now see how it could happen. I may have been right before and am now wrong. But one thing is for sure, I'll probably err on the side of caution.

 

[tmajor]

But one thing is for sure, I'll probably err on the side of caution.

I think, all situations are different, but being "aware and cautious" is a prudent move. Some other things are just "obviously dumb".

 

[Short Game]

...being "aware and cautious" is a prudent move.

Sometimes I kind of miss that aware part.

 

[tungularafishcamp]

When I pull skiffs uphill from the fel it will lift one or both rear wheels off the ground even with the backhoe on. I usually grab a piece of piling in the backhoe for a little more weight but you still have to watch it.
Rick

 

[Short Game]

Whoa, those are some serious skiffs!

 

[tungularafishcamp]

the 20 ' is about 2700 lbs without the net in it,
Rick

 

[alchemysa]

Wow. Has there ever been a faster growing thread on TBN? From 0 to 348 posts in less than 2 weeks.

 

[tmajor]

There is at least one more thing, which should be considered.

Repeated operations could differ, one from the other. I'm thinking about skidding logs, for instance. Just because one log was skidded without incident, doesn't mean the next log will skid the same. It could roll differently, while going around a tree, and get snagged on the tree. Or the last log may have exposed a rock, which will snag the next. You get the picture. "Every pull, is a new adventure".

 

[RoyJackson]

While I never gave the back flip much thought, it seemed that I believed that if your pulling point was lower than the rear axle, it would not happen. This thread made me rethink the problem and that rethinking is what changed my mind. I can now see how it could happen. I may have been right before and am now wrong. But one thing is for sure, I'll probably err on the side of caution.

There's been a lot more armchair engineering then fact on this thread, but your drawbar provides the hook up that is least likely to result in a rear rollover...reducing the possibility to negligible on a level surface. Slopes...well, a different issue altogether (moves your tractor's center of gravity)...same with trying to jerk a pull to get it moving.
Use some common sense and have a bit of respect for your equipment.