Preventing tractor back flip

[arsenix2001]

And as far as "stuff up front" goes I'm not talking about a welded hook on a loader bucket, the front of the frame on most tractors is just as strong as anything attached to the rear of the tractor including the rear axle assembly like the draw bar.

i would differ on opinion to this statement. Most ag tractors unlike industrial tlbs basically hold the front and back together via the transmission to the rear axle, and perhaps loader braces. Tlbs have a dedicated subframe. When using the drawbar, its attached to the rear axle where most tractive force takes place. Pulling from the front with enough rear traction can put undue stress on the tractor. This is a balls to the wall hard pulling senario tho, as in repeated snatches bacwards under heavy power.

 

[LD1]

I'm curious, just how many times or instances do you use YOUR tractor to PULL something that is likely to cause a "back flip"

Not very often. I have been doing what I have been doing for MANY years. Not trying to sound arrogant, but I have never came close. And I have latched onto and skidded, or tried to skid logs that were just too big.

And I usually do it by chaining short and onto the 3PH, that way I can raise the log up out of the mud/dirt, and add a little weight to the back for traction. But with the loader out front, there is little chance of going over. But I an not reccomending anyone else do this either.

 

[xtn]

He made at least one major wrong choice or several smaller ones that added up. The most efficient wrong choice would be to pull from the top link or its mount on the tractor.
larry

Heck, might as well pull from the top of the ROPS. Yes, pulling from above the rear axle is much more efficient way to flip, as the tractor only needs to crawl out from under the attachment point instead of wrapping itself backwards over it.

 

[LD1]

i would differ on opinion to this statement. Most ag tractors unlike industrial tlbs basically hold the front and back together via the transmission to the rear axle, and perhaps loader braces. Tlbs have a dedicated subframe. When using the drawbar, its attached to the rear axle where most tractive force takes place. Pulling from the front with enough rear traction can put undue stress on the tractor. This is a balls to the wall hard pulling senario tho, as in repeated snatches bacwards under heavy power.

BINGO.

While the frame up front may look all beefy and strong, it probabally doesnt go much past the motor. If you look, most tractors transmission-rear end connection is just the castings. NO frame.

And even on the tractors I have seen that have 1/2 frame, there reallt is no good place to even hook without adding some sort or hook or something??

Either way, its just not good on the tractor. But I guess its a good thing you cannot get maximum tractive force by doing this, or you probaballly really mess someting up.

 

[RoyJackson]

Can you please address the part of my post that was addressed specifically to you?

xtn

What was written was all the posts were based upon certain assumptions with little personal experience or any empirical data. That included my posts...not that you posted anything directed toward me, personally. I've never had a rear roll over...have you? The only time my front tires ever came off the ground had nothing to do with pulling from the draw bar.
The professor most likely had more statistical data resulting from actual rear rollovers and greater knowledge of tractor design and dynamics.

Your comment in an earlier post about the professor generalizing...well, what do you think you're doing? Exactly the same thing...generalizing. The difference is the professor has more credibility.

 

[Farmwithjunk]

Have you ever witnessed it happen? On level ground, with a slow and steady pull, and a drawbar mounted below the axle?

I wasn't there to see it happen, but I WAS there to help extricate the trapped victim....

Years ago, IIRC around 1982, while on the Fire Dept, I made a run where a man was killed on a JD4020 that flipped backwards. He was trying to pull a stuck combine out of the mud. All the "rigging" was still in place. He had a piece of cable between the fixed drawbar and the steering axle of the combine. It was roughly 25' long. There was one witness. He was in the cab of the combine. He told us the tractor started pulling, then the combine quit moving after a couple feet, then he looked out the rear window just in time to see the hood of the tractor come up and over. It was a 4020 PowerShift, narrow front, no front weights, but quite a few rear wheel weights..... There was nothing to indicate the operator was jerking on the combine, which was verified by the man in the combine. The tractor was found in 2nd gear, but due to the nature of the rollover, could have possibly been in another gear at the time of the accident, shifter being moved as tractor hit the ground, OR while rescue techs worked to free the man. It was the first rescue run I made where there was a fatality, so it sticks in my mind to this day.

The state medical examiner and the Fire Marshal released their statements a few days after the fact. They had a couple engineers specializing in accident reconstruction to look over the findings. Their comments were included. They said so long as the hitch point on the tractor was above the traction point (tires to ground) there was a possibility of rear rollover. Seeing a dead man pinned under the fender of a tractor every time you close your eyes for a few days cements that finding, let me tell ya.

It CAN HAPPEN (and DOES happen, however rare....) in spite of all the theories stating how impossible this is.

While in my freshman year of college, I was on a debating team. I read (with great interest) a transcript of a debate where a woman argued that the earth was flat. It was VERY convincing. (VERY....) She made her points so convincingly, her opponent finally had no response. So even armed with the unquestionable knowledge that the earth ISN'T flat, a good theory and a better debater can make a case against "facts". I see a LOT of that here in this thread, albeit not quite as convincing...... with the knowledge that back-flipping a tractor (while pulling from a low point) IS possible and has happened. Granted....ALL the stars must align properly, and slow operator response is probably a major contributing factor.....Still, no theories to the contrary will be good enough to win this debate.

 

[SPYDERLK]

I wasn't there to see it happen, but I WAS there to help extricate the trapped victim....

Years ago, IIRC around 1982, while on the Fire Dept, I made a run where a man was killed on a JD4020 that flipped backwards. He was trying to pull a stuck combine out of the mud. All the "rigging" was still in place. He had a piece of cable between the fixed drawbar and the steering axle of the combine. It was roughly 25' long. There was one witness. He was in the cab of the combine. He told us the tractor started pulling, then the combine quit moving after a couple feet, then he looked out the rear window just in time to see the hood of the tractor come up and over. It was a 4020 PowerShift, narrow front, no front weights, but quite a few rear wheel weights..... There was nothing to indicate the operator was jerking on the combine, which was verified by the man in the combine. The tractor was found in 2nd gear, but due to the nature of the rollover, could have possibly been in another gear at the time of the accident, shifter being moved as tractor hit the ground, OR while rescue techs worked to free the man. It was the first rescue run I made where there was a fatality, so it sticks in my mind to this day.

The state medical examiner and the Fire Marshal released their statements a few days after the fact. They had a couple engineers specializing in accident reconstruction to look over the findings. Their comments were included. They said so long as the hitch point [[on the tractor]] was above the traction point (tires to ground) there was a possibility of rear rollover.

It CAN HAPPEN (and DOES happen, however rare....) in spite of all the theories stating how impossible this is.

While in my freshman year of college, I was on a debating team. I read (with great interest) a transcript of a debate where a woman argued that the earth was flat. It was VERY convincing. (VERY....) She made her points so convincingly, her opponent finally had no response. So even armed with the unquestionable knowledge that the earth ISN'T flat, a good theory and a better debater can make a case against "facts". I see a LOT of that here in this thread, albeit not quite as convincing...... with the knowledge that back-flipping a tractor (while pulling from a low point) IS possible a has happened. Granted....ALL the stars must align properly, and slow operator response is probably a major contributing factor.....Still, no theories to the contrary will be good enough to win this debate.

How long and high was the drawbar? Did it bend upward? Im not asking for specific measurements, but instead to hilite parameters that matter. The explanation given by the examiners is not supported by Physics. I expect the true cause escaped everyone.

Since it happens under some sort of unknown condition, I wonder why a demonstration of the phenomenon is not done with real documentation so wed be able to see the problem instead of attributing it to capricious occurrence. Its just magic ...

I would sure like to see that flat earth debate.
larry

 

[tmajor]

Reading that story, brings a couple of things to mind.

Thinking of my own experience, I'm guessing that many of us, who have pulled such things, may have come closer to flipping the tractor, than we realize.

I'd say that the fact, that the combine stopped, was the key to the accident. My mental process always seemed like, "start slowly, so as not to break traction", then once you are moving, "give it some gas to keep the momentum up". At this point, a sudden stop, caused by the pulled object, could be "sudden death" or injury (if you are lucky).

 

[SPYDERLK]

Reading that story, brings a couple of things to mind.

Thinking of my own experience, I'm guessing that many of us, who have pulled such things, may of come closer to flipping the tractor, than we realize.

I'd say that the fact, that the combine stopped, was the key to the accident. My mental process always seemed like, "start slowly, so as not to break traction", then once you are moving, "give it some gas to keep the momentum up". At this point, a sudden stop, caused by the pulled object, could be "sudden death" or injury (if you are lucky).

Absolutely. Could cause a very quick back tip that proceeded past the driven point soley by inertia.:thumbsup: ... altho quick deceleration of the tractor mass from the height of the drawbar favors a quick transient shift of weight to the front. But with the engine at full song its ready to grunt and rare it up fast.
larry

 

[tmajor]

Absolutely. Could cause a very quick back tip that proceeded past the driven point soley by inertia.

Actually, in addition to "inertia", if the combine stopped and the tractor tires stopped due to good traction, the tractor drive system would actually power the tractor mass backwards around the drive axle.

 

[SPYDERLK]

Actually, in addition to "inertia", if the combine stopped and the tractor tires stopped due to good traction, the tractor drive system would actually power the tractor mass backwards around the drive axle.

Sure, but weve addressed the Physics imposed inhibitions on that above ... and in other threads. Over and over. The seeming fact that this is seen very seldom leads me to believe there is some specific difference that occurs in these instances. It would be good to see some good documentation -- or indeed any worthy of the word.
larry

 

[Short Game]

If it comes down to an article of faith or a question of belief, I'm going with, "it can happen." It doesn't cost me anything. I just wish it would make me tax-free. Believing it can't happen has a potential cost that I would not want to bear. And so:

I believe!​

Can I get, Amen?!?​

 

[SPYDERLK]

If it comes down to an article of faith or a question of belief, I'm going with, "it can happen." It doesn't cost me anything. I just wish it would make me tax-free. Believing it can't happen has a potential cost that I would not want to bear. And so:

I believe!​

Can I get, Amen?!?​

Its just as important to know what circumstances make it possible and what can be done to prevent it so you dont have to be excruciatingly careful all the time.
larry

 

[Farmwithjunk]

How long and high was the drawbar? Did it bend upward? Im not asking for specific measurements, but instead to hilite parameters that matter. The explanation given by the examiners is not supported by Physics. I expect the true cause escaped everyone.

Since it happens under some sort of unknown condition, I wonder why a demonstration of the phenomenon is not done with real documentation so wed be able to see the problem instead of attributing it to capricious occurrence. Its just magic ...

I would sure like to see that flat earth debate.
larry

Actually, the accident report EXPLAINED the physics involved to everyones satisfaction... Hitch point higher than ground contact point (...sufficient traction so as not to stop the tractor...enough torque supplied to rotate tractor around axle.....tied to object [combine] that was virtually "immovable" by virtue of being mired down deep in mud) .....and that was done by professionals (engineers) who made their living at that time by doing accident reconstruction. They were very familiar with machinery, seeing as to how they had done literally hundreds of investigations into mining accidents involving machinery. (Ky is a coal state) There never was any attempt to explain it away as "just magic". A solid, conclusive cause was found.

Physics as one interprets them to explain their opinion or agenda, and physics as they are used to explain reality as it plays out in everyday life are often two different concepts. The fact of the matter is, tractors CAN and DO flip backwards, sometimes in less than "incredible circumstances". At that point, one needs to stand back and take a long look at how their interpretation of applied physics fails to sync with simple facts. And far too often, people limit their view of facts to what they WANT to see, blinding their vision of what all there is to see. Most of this thread is pure conjecture, and very much an attempt to rationalize a number of personal opinions.

It doesn't go unnoticed that we have a number of engineers on BOTH sides of the issue. Both sides have perfectly good rationale' as to why they believe what they believe. Toss in the FACT that tractors do occasionally flip backwards, and it's hard to see the validity in any argument that says it can't happen.

As for the circumstances of the accident;

We used one rear axle (left side) and the drawbar as lift points when we winched the tractor up to remove the body. I was one of the firefighters doing the rigging. (We had a military wrecker to lift with...) I don't recall the draw bar as having ANY bend in it. It was a straight draw bar (no offset up or down) On 4020's equipped with 34" rear tires, that drawbar is normally around 14". It extends roughly 12" to 14" behind the pto stub. The man killed was a hired hand on the farm where the accident occurred. This was in the days when OSHA was building their reputation. State medical examiners reports were reviewed by OSHA and found to be accurate and no fault was placed on farm owner/tractor manufacturer/ect....Plain and simple....These things happen. It was an accident.

I'm digging around in what fire dept archives I have access to, trying to find any more info, but early 80's is a little bit "pre computer era" in our FD. I've got a call in to the current chief, hoping he can supply me with written copies if they still exist, but even with that, enough time has passed where I'm trusting most of this to memory.

 

[Short Game]

Its just as important to know what circumstances make it possible and what can be done to prevent it so you dont have to be excruciatingly careful all the time.
larry

So, I chain the front of my tractor low to a tree and pull from the rear with a winch and a block. 24,000 pounds max with a single block is more than I could easily get on that draw bar and traction.

Early one morning, my neighbor up the road called me up. The school bus blew the trunaround at his place at the end of the road. The driver (one of my bestest old friends) had backed the rear wheels over the edge of the creek bank (a ten foot drop to the water). I didn't know what I'd find when I got there with my 27HP Cub Cadet. One look and I had to laugh. The best I could do would be get the bus to rocking and have it go over the edge and launch my little tractor in the deal. I had to take a pass at the cost of my friend's embarrassment. I couldn't pull his bus, much less, his chestnuts out of the fire. It took and anchored wrecker.

I try not to bite off more than I can chew. This tendency comes with age, if it comes in time.

 

[caspar3259]

I don't know if this thread is still on the tractor flip question, but here's my simplified view:

Assuming the tractor motor does not stall and nothing breaks... the motor turns the axle and the axle turns the wheel. Something must turn. If the wheel turns easier than the tractor, then you move forward or spin your wheels. If the tractor turns easier than the wheels, then the tractor rotates.

Another way to look at it: imagine you have a battery powered toy tractor. Grab the body and turn it on --> the wheels turn. Now grab the wheels and turn it on --> the tractor turns.

-Jeff

 

[SPYDERLK]

Actually, the accident report EXPLAINED the physics involved to everyones satisfaction... Hitch point higher than ground contact point (...sufficient traction so as not to stop the tractor...enough torque supplied to rotate tractor around axle.....tied to object [combine] that was virtually "immovable" by virtue of being mired down deep in mud) .....and that was done by professionals (engineers) who made their living at that time by doing accident reconstruction. They were very familiar with machinery, seeing as to how they had done literally hundreds of investigations into mining accidents involving machinery. (Ky is a coal state) There never was any attempt to explain it away as "just magic". A solid, conclusive cause was found.

[[Physics as one interprets them to explain their opinion or agenda, and physics as they are used to explain reality as it plays out in everyday life are often two different concepts. The fact of the matter is, tractors CAN and DO flip backwards, sometimes in less than "incredible circumstances". At that point, one needs to stand back and take a long look at how their interpretation of applied physics fails to sync with simple facts. And far too often, people limit their view of facts to what they WANT to see, blinding their vision of what all there is to see. Most of this thread is pure conjecture, and very much an attempt to rationalize a number of personal opinions.] ......This does not mean that the physics is wrong. It means than some assumed conditions of the situation are not right. Thats why we need documentation.

It doesn't go unnoticed that we have a number of engineers on BOTH sides of the issue. Both sides have perfectly good rationale' as to why they believe what they believe. Toss in the FACT that tractors do occasionally flip backwards, and it's hard to see the validity in any argument that says it can't happen.

As for the circumstances of the accident;

We used one rear axle (left side) and the drawbar as lift points when we winched the tractor up to remove the body. I was one of the firefighters doing the rigging. (We had a military wrecker to lift with...) I don't recall the draw bar as having ANY bend in it. It was a straight draw bar (no offset up or down) On 4020's equipped with 34" rear tires, that drawbar is normally around 14". It extends roughly 12" to 14" behind the pto stub. The man killed was a hired hand on the farm where the accident occurred. This was in the days when OSHA was building their reputation. State medical examiners reports were reviewed by OSHA and found to be accurate and no fault was placed on farm owner/tractor manufacturer/ect....Plain and simple....These things happen. It was an accident.

I'm digging around in what fire dept archives I have access to, trying to find any more info, but early 80's is a little bit "pre computer era" in our FD. I've got a call in to the current chief, hoping he can supply me with written copies if they still exist, but even with that, enough time has passed where I'm trusting most of this to memory.

Mulling it over in my head I thot of another definite contributory factor in your described incident. The long cable. Cables are lighter than chains and use stonger steel "fibers" more highly stressed for a given load. This, plus the cable lay results in the cable stretching elastically more than a chain would. This ensures that the cable would pull further back after max force drops off. This would slow the rate that force dropped as it rebounded. It is more likely than with chain that this force would be maintained long enuf to snap the nose up high.

Thanks for some of the pertinent info on the drawbar. As for what the engineers said, I would have to see it to decide whether it was correct. What you have relayed from memory does not close the loop on critical considerations and does relay a statement that is incorrect in fact or by omission, perhaps incorrectly.

I havent seen that anybody has said that a tractor will not flip backward.
larry

 

[LD1]

Another way to look at it: imagine you have a battery powered toy tractor. Grab the body and turn it on --> the wheels turn. Now grab the wheels and turn it on --> the tractor turns.

-Jeff

That is correct, but no one is saying a tractor cannot flip al by itself if the tires are locked(like frozen in ice).

But now take a chain and affix to a drawbar BELOW the axle of that tor tractor. And attach that chain to something solid. Grab the wheels and now see what havvens??? The chain drawn up tight (behind and BELOW the axle) counters the nose comming up. Ib the chain dont break, the nose will NOT go on over unless the tractor goes backwards toward the chain. Which is counter-intuitive because the tractor is driving the other diraction.

 

[Short Game]

Interesting thought about the differences between cable and chain. The elasticity could be a killer. Definitely adds another force vector. Time is also a solid factor (when what happens, when forces are rising or falling). Small fractions of seconds can make big differences when big forces balance against each other. What do they call it, a "tipping point?" In the case of this question, the tipping point could be when the front wheels are three inches off the ground (or less).

Using my winch, I always fear a rigging failure. It would be hard to jump fast enough.

 

[crash325]

http://agecon.uwyo.edu/RiskMgt/humanrisk/TractorOverturnhazardspdf.pdf

End of discussion. ,:laughing::laughing::laughing::thumbsup::thumbsup::thumbsup: