Preventing tractor back flip

[SPYDERLK]

sorry to repeat; check out 50 seconds into Backflip With Tractor - YouTube

That is a tractor flipping over on an incline. He essentially popped a wheelie and got his Center of Mass behind his rear axle. He wasnt pulling anything from the drawbar, but even if he was, steep inclines can overcome the backtip stabilization offered by a drawbar. Use a long drawbar and a steady slow pull if youre pulling on a greater than ~10ｰ incline
larry

 

[SPYDERLK]

Note, in the video Backflip With Tractor - YouTube that the tractor that flips has a drawbar ...and, given the momentum generated, it simply digs in lifts the rear wheels a little but doesn't stop the flip.

Different situation - steep hill popping wheelies. Its NOT a wheelie bar. Just because it is possible to make informedly negatively optimized choices in drawbar length and situation does not categorically defeat the effectiveness of the concept. The tractor wasnt pulling anything so the drawbar didnt come into play for its intended function at all. If it had extended further backward and had a bearing plate on the end it could have acted as a wheelie bar. In that case - with that operator the tractor would have rared up and tipped sideways or hed still be trying.
larry

 

[SPYDERLK]

Larry...do you design tractors? Do you...other then theory, know anything about tractor design and the dynamics involved?
Although I'm in Quality Assurance (not design...automotive and (currently) aerospace, but not tractor specifically), I did a fair amount of study on safe usage of a tractor as I didn't want to become an unfortunate statistic. Does that make me an expert on tractor design...nope...but it does make me a very knowledgeable owner of tractors.

As far as your previous threads...once they're off the first page of a forum...I doubt anyone reads or has knowledge of them (BTW, that applies to all posters, not just you). This topic has gone on (now and then) for at least 10 years...sort of like the "HST vs. Gear" debates.

Are you arguing logic or innuendo? The topic has gone on and been solved. For those who actually understand it to laboriously sort the top of the head statements anew and defuse every important missed nuance takes time, again, that was invested previously. Thats why links are given -- FREE; no searching. It is Physics ... and its correct interpretation is important to everyone as a realistic safety and capability tool. -- Unlike HST vs Gear which is based loosely on a hodgepodge of preference, attitude, and fact. There is no answer there.
larry

 

[xtn]

No such thing as 100% safety. Too many variables (such as topography).

Anyway, the drawbar, as designed below the rear differential, is the lowest part of the tractor....and the safest place to hitch for pulling.
There is no way for the restraining force can be below the contact patch of the tires. Physically impossible...we're discussing real life considerations, not theory, correct?

Correct. I pointed out that the drawbar being underground prevents front end lift. You now point out that this configuration isn't normally possible. Put those two facts together and you're left with front end lift.

To be more accurate the position of the drawbar is not directly a concern. Rather it is indirectly a concern only inasmuch as it effects the vector of the restraining force. It IS possible to get that vector to point under the tires' contact patch without the drawbar going underground itself. This is the condition described by your second link in the section titled Drawbar Leverage, where it talks about the fact that the drawbar position is normally designed to get closer to the ground as the nose of the tractor rises. The design intent is such that as the nose lifts, the angle of your chain will end up pointing below the tires' contact patch before the tractor has tilted so far back that it will flip. So it's a self limiting danger.

Self limiting danger of flipping, but NOT preventing the tractor from raising its nose just because the drawbar is below the axle, which is what you claimed. So as civilly as possible, and without any personal judgment, you are wrong.

And speaking towards the larger question of whether the tractor could flip... Yes it could. There are a lot of factors working against it, but if one were to get the nose shooting up with enough momentum one could have enough rotational force to overwhelm those forces working against it.

 

[ctgoldwing]

The only way to completely prevent rearing up is you have a drawbar on the ground at the level of the tires but that isn't practical.

I'm with this answer . . .

assuming you have unlimited power to deliver to the rear drive wheels at some point the force will be reached that will overcome the moment force keeping the tractor front down.

 

[milkman636]

"If the rear axle should be unable to rotate, the tractor chassis
rotates about the axle. This reverse rotation results in the
front-end of the tractor lifting off the ground until the
tractor's CG passes the rear stability baseline. At this
point the tractor will continue rearward from its own
weight until it crashes into the ground or other obstacle."

"It is also possible to flip a tractor
rearward when the load is properly hitched to the drawbar."

Direct quotes taken from Roy's posted link to the University of Wyoming:http://agecon.uwyo.edu/RiskMgt/humanrisk/TractorOverturnhazardspdf.pdf

The section starting on page two titled "Rear-Axle Torque" pretty well answers the question.

 

[SPYDERLK]

"If the rear axle should be unable to rotate, the tractor chassis
rotates about the axle. This reverse rotation results in the
front-end of the tractor lifting off the ground until the
tractor's CG passes the rear stability baseline. At this
point the tractor will continue rearward from its own
weight until it crashes into the ground or other obstacle."

"It is also possible to flip a tractor
rearward when the load is properly hitched to the drawbar."

Direct quotes taken from Roy's posted link to the University of Wyoming:http://agecon.uwyo.edu/RiskMgt/humanrisk/TractorOverturnhazardspdf.pdf

The section starting on page two titled "Rear-Axle Torque" pretty well answers the question.

If you are pulling against a load attached to a fixed drawbar extending beyond the tire circle the end of the drawbar will touch down ... at which point the pull point will be at ground level and stop driving the tip. Unless the tractor is rearing up fast the tip will stop and the engine will stall.
larry

 

[RoyJackson]

Self limiting danger of flipping, but NOT preventing the tractor from raising its nose just because the drawbar is below the axle, which is what you claimed. So as civilly as possible, and without any personal judgment, you are wrong.

Not wrong...just pursuing the real life scenarios rather then the theoretical.

So, to put it in a way that works better...hitching to the drawbar reduces the possibility of a rear rollover as much as possible with the current design of tractors (as we define tractors on TBN).

 

[RoyJackson]

Are you arguing logic or innuendo? The topic has gone on and been solved.
larry

Not arguing with anything...and I'm sure this subject will arise again on TBN. Might be different players involved, that's all...

So, has the issue been resolved? Well, read some history on TBN and you'll find it was "resolved" years ago. But like most forums, some topics come up repeatedly and this is one of them.

 

[xtn]

Not wrong...just pursuing the real life scenarios rather then the theoretical.

So, to put it in a way that works better...hitching to the drawbar reduces the possibility of a rear rollover as much as possible with the current design of tractors (as we define tractors on TBN).

That assessment is generally correct. But you were wrong to say that the drawbar being lower than the axle means the front end is forced down, and you were wrong to tell me I was wrong when I explained why it isn't true.