Preventing tractor back flip

   / Preventing tractor back flip #271  
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
 
   / Preventing tractor back flip #272  
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?!?​
 
   / Preventing tractor back flip #273  
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
 
   / Preventing tractor back flip #274  
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.
 
   / Preventing tractor back flip #275  
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.
 
   / Preventing tractor back flip #276  
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
 
   / Preventing tractor back flip #277  
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
 
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   / Preventing tractor back flip #278  
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.
 
   / Preventing tractor back flip #279  
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.
 

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