Preventing tractor back flip

[looknlearn]

Here is a article that I stole from another thread on TBN that talks about flipping from a load.
It may help or muddle but here it is. Near the end is when it talks about what happens when pulling on an immovable object.
Tractor Overturn Hazards


EDIT: Oopps sorry looks like I posted at the same time as crash325.

 

[SPYDERLK]

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.

Yeah, Im thinking rebound can be a big thing in initiating an extremely rapid backtip. I think the backflip possibility from a [fixed] drawbar comes down to :
a] Length of the drawbar behind the axle,
b] Height of the drawbar
c] Diameter of the tires,
c] Drive speed
d] Stored energy in the tether.

The 1st 3 govern the angle of tractor body at which the pull point comes to earth and the tip is no longer driven by tether force but is in coast mode. -- The 1st 4 tell how fast the tip can proceed. The last has the ability to accelerate the tip, particularly if a jerk happens storing more energy that then feeds into the tip after the tractor slows.
If coast mode occurs at too high a tip point the tractor can easily pass the balance point and continue over. If coast occurs lower it takes a lot of tip speed to coast over [not to mention that this drawbar length will probably take the pullpoint underground and actively resist the tipping].
Very important to note is that where no slip occurs the tipping speed will increase as the end of the drawbar lowers to the coast point. Even tho further tip past this point is resisted by both COG and drive force it may be too late with some configurations and speeds. Keep the drawbar long when you do hard pulling. Go slow. The best safe hi pull force will come form a long drawbar with its tip on the ground. Steering brakes.
larry

 

[crash325]

Here is a article that I stole from another thread on TBN that talks about flipping from a load.
It may help or muddle but here it is. Near the end is when it talks about what happens when pulling on an immovable object.
Tractor Overturn Hazards


EDIT: Oopps sorry looks like I posted at the same time as crash325.

These folks are having too much fun and it will never end, :laughing::laughing:

Not going to let something like facts get in the way. :laughing::laughing::laughing:
:thumbsup:

 

[RoyJackson]

These folks are having too much fun and it will never end, :laughing::laughing:

Not going to let something like facts get in the way. :laughing::laughing::laughing:
:thumbsup:

Yep, armchair engineering at it's finest...

 

[Farmwithjunk]

Yep, armchair engineering at it's finest...

Yep....The ol' "It can't possibly happen even though it HAS happened, just because I can't understand WHY it happened" syndrome in action......

 

[xtn]

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.

Yup, the chain being below the axle results in less leverage to raise the nose. Yup, the lower it goes, the lower the leverage gets. No, it never reaches zero unless the connection point gets to the ground. To be fair I will say that when it gets close to the ground, the leverage to raise the nose is so slim that any tractor of standard configuration would need unreasonably high power to lift its nose off the ground.

Of course by the time it gets that low, the nose is already well up in the air, bringing the required power level back into a possibly reasonable level.

And remember that although it may be counterintuitive, if the nose comes up even an inch, the axle and tires have already moved rearward towards the load. So no matter how counterintuitive it may be, that is what is happening.

 

[RoyJackson]

Yep....The ol' "It can't possibly happen even though it HAS happened, just because I can't understand WHY it happened" syndrome in action......

Anything can happen, at any time...all one can do is try to lower their risk.
Some of the scenarios and justifications on this thread have gone a tad over the top...

 

[SPYDERLK]

Yep, armchair engineering at it's finest...

Yep....The ol' "It can't possibly happen even though it HAS happened, just because I can't understand WHY it happened" syndrome in action......

The ol' Magical Cause Syndrome. Leads to better understanding of everything that is not obvious.

 

[xtn]

An elastic connection does not add another "vector." What it does do is reduce the energy going into the tip-up during the stretch, stores that energy, and add that energy back into the tip-up during the rebound. To be perfectly accurate it probably converts and wastes a bit of the energy as heat.

So when it adds tip-up energy back to the tractor during the rebound, that may make enough difference to flip the tractor. But if that is so, a bit more power from the engine could do the same thing without the elastic hookup.

So anybody who says a tractor cannot flip with an inelastic chain, but could with an elastic cable, is admitting that a tractor with enough power to lift itself, against the decreasing leverage of the load as the drawbar lowers, can flip with an inelastic chain.

 

[Short Game]

The vector I was speaking of was the tractor end of the cable moving back toward the load. I have loaned some chains and had them come back to me stretched (a.k.a., ruined). Not much rebound in them. The cable gives the tractor a way to multiply the tipping force over the time it is storing its power in the cable. This could be a huge factor and the difference between flipping and not flipping.

When I lived on the beach and had my little '51 flathead four Jeep, I could pull just about anything out of the high sand, trucks, Caddies, you name it. I had 100 feet of 3/4" polypropylene line. My little Jeep would take a low gear run and use its power to store force in the stretched line. About the time I could pull no farther, I'd lock the brakes and the stretched line would snap the Caddy out of the soft sand.

 

[SPYDERLK]

An elastic connection does not add another "vector." What it does do is reduce the energy going into the tip-up during the stretch, stores that energy, and add that energy back into the tip-up during the rebound. To be perfectly accurate it probably converts and wastes a bit of the energy as heat.

So when it adds tip-up energy back to the tractor during the rebound, that may make enough difference to flip the tractor. But if that is so, a bit more power from the engine could do the same thing without the elastic hookup.

So anybody who says a tractor cannot flip with an inelastic chain, but could with an elastic cable, is admitting that a tractor with enough power to lift itself, against the decreasing leverage of the load as the drawbar lowers, can flip with an inelastic chain.

In a situation where there is ample power and traction to pull a load, but then the load stops dead the tractor tends to nose down under deceleration and then back upward under power after it stops decelerating. Stored energy will give it an extra kick to speed the backtip ... perhaps enuf to take it over.
larry

 

[Egon]

And remember that although it may be counterintuitive, if the nose comes up even an inch, the axle and tires have already moved rearward towards the load. So no matter how counterintuitive it may be, that is what is happening./QUOTE]

Nothing counterintuitive about it but lets say the distance between the tire and the load will become shorter. The tire, the load or both can be involved in the movement.:thumbsup::thumbsup:

 

[IronHog]

So you're saying there's a chance.


(Dumb & Dumber reference there)

Oh yea.

I think you could ride a powerful tractor over easy logging off the 3 pt hitch.


But you'd hafta keep the RPM's up and either be a careless or bad operator.



I'm much more concerned about the tractor rolling on me while hooking up tongs, a stick coming into the rack, or getting a hand crushed/cut while logging. Flipping backwards is a more theoretical than actual risk in my particular situation.

I need to take some pics next time we bank a load or two. True logging with a tractor is pretty much a dying art around most parts.

 

[Short Game]

True logging with a tractor is pretty much a dying art around most parts.

Well, for me it must have been a flourishing science today, even if it wuz some poor production. I dragged out two skinny 90 foot alders and bucked them into 12' 6"s, and lifted them on my bucking forks and made them into 15 inch pieces. I prefer the fat trees, but the power company dropped these and a few others with my permission because they threatened their power line. I dragged them uphill by the receiver hitch in the middle of my box blade and I didn't even flip over backwards.

 

[Farmwithjunk]

The ol' Magical Cause Syndrome. Leads to better understanding of everything that is not obvious.

Nothing "magical" about it....for MOST of us anyway....and not that difficult to understand provided one's head is not buried in the sand.

 

[xtn]

The vector I was speaking of was the tractor end of the cable moving back toward the load. I have loaned some chains and had them come back to me stretched (a.k.a., ruined). Not much rebound in them. The cable gives the tractor a way to multiply the tipping force over the time it is storing its power in the cable. This could be a huge factor and the difference between flipping and not flipping.

When I lived on the beach and had my little '51 flathead four Jeep, I could pull just about anything out of the high sand, trucks, Caddies, you name it. I had 100 feet of 3/4" polypropylene line. My little Jeep would take a low gear run and use its power to store force in the stretched line. About the time I could pull no farther, I'd lock the brakes and the stretched line would snap the Caddy out of the soft sand.

That is not "another" vector. That's the same vector we've been working with the whole time. And I know what you mean but you're saying it wrong; the cable adds energy to the tip during the time it is rebounding, not while it is stretching.

What you did with your jeep is commonly referred to as snatching. If you think about the dynamics you will recognize that the energy is stored during the stretch, and added back in during the rebound.

 

[xtn]

In a situation where there is ample power and traction to pull a load, but then the load stops dead the tractor tends to nose down under deceleration and then back upward under power after it stops decelerating. Stored energy will give it an extra kick to speed the backtip ... perhaps enuf to take it over.
larry

Basically, yes. According to LD1 this could never happen, as it will obviously bring the nose up AND pull the tractor backwards towards the load. He thinks that combination of movements is not possible.

 

[tmajor]

What you did with your jeep is commonly referred to as snatching. If you think about the dynamics you will recognize that the energy is stored during the stretch, and added back in during the rebound.

I believe, this can happen with "chain", also. I was getting my truck pulled out of a snow bank, when the chain broke. The chain flew back, took out the bug deflector and the windshield. It seems, like it should have just fallen on the ground.

 

[xtn]

The tire, the load, or both can be involved in the movement.

Sure, except when we're dealing with an immovable load....

 

[xtn]

I believe, this can happen with "chain", also. I was getting my truck pulled out of a snow bank, when the chain broke. The chain flew back, took out the bug deflector and the windshield. It seems, like it should have just fallen on the ground.

Sure. Nothing in our world is completely inelastic.