Preventing tractor back flip

[alchemysa]

See the simplified diagram below.

If "A" moves forward, "E" will rise.

Bruce

On a real tractor 'B' 'D' and 'A' are not fixed in one plane.
D is fixed to B, but A rotates independently around B. So A could go forward or backward without B moving.


I think something is wrong with your idea but I don't quite know what. Nevertheless I do agree it could flip... as I said in my previous post.

 

[JoeL4330]

could it help to look at some conditions "at the limit"?

1) The drawbar is a lever arm: suppose there were sufficient weight pulling straight down? I suspect the tractor would turn about the rear axle.

2) The rears normally rotate and the axle-housing is stationary: suppose you had enough torque, everything was strong enough not to break, and the rears were immoveable? I suspect the axle housing (and thus, the tractor) would rotate.

So, in the limit, it seems like there can be situations where rotation is initiated ...and, if there is sufficient momentum and nothing to stop the rotation, over she'd go, right?

I can imagine that trying to go up a sufficiently steep incline, with enough torque, would cause the tractor to "counter-rotate".

just my thoughts

[of course, one should still always pull forwards, from the drawbar and not from some higher fixture ...if you tried to pull a relatively immoveable object backwards from a high FEL attachment point, the rears would come up, no? That is the tractor would count-rotate around the front axle ...that is, until the bucket smacked into the ground]

 

[k0ua]

could it help to look at some conditions "at the limit"?

1) The drawbar is a lever arm: suppose there were sufficient weight pulling straight down? I suspect the tractor would turn about the rear axle.

2) The rears normally rotate and the axle-housing is stationary: suppose you had enough torque, everything was strong enough not to break, and the rears were immoveable? I suspect the axle housing (and thus, the tractor) would rotate.

So, in the limit, it seems like there can be situations where rotation is initiated ...and, if there is sufficient momentum and nothing to stop the rotation, over she'd go, right?

I can imagine that trying to go up a sufficiently steep incline, with enough torque, would cause the tractor to "counter-rotate".

just my thoughts

I have heard of (not seen) of rear tires frozen to the ground after rain and freezing temps causing the tractor to instantly flip as soon as the clutch was engaged, and going up a steep incline, every tractor becomes light in the front, so the likleyhood of a flip becomes greater.

James K0UA

 

[Farmwithjunk]

While the theories are bouncing around....It may be worth mentioning that there have been hundreds, if not thousands of cases where tractors HAVE flipped backwards when pulling from a low mounted draw bar. The fact that it DOES happen with some minor degree of regularity SHOULD influence the possible v impossible voting.

 

[Tx Jim]

The higher the hitch point the easier it will be for front wheels to raise off the ground therefore being easier to FLIP. If a tractor has enough HP and traction it will flip no matter how low the load is attached. Just look a the puller tractors that are required to have wheely bars

 

[psj12]

As long as the contact point of the tires and ground are lower than the tow point leverage exists that lifts the front. The closer thay are to gether the less likley it is to happen.

 

[xtn]

As long as the contact point of the tires and ground are lower than the tow point leverage exists that lifts the front. The closer thay are to gether the less likley it is to happen.

Some of you keep mentioning a relationship of the axle height to the drawbar. Not important.

You've got force #1, the contact patch of the rear tires on the ground trying to push forward. And you've got force #2, the attachment at the drawbar trying to pull backwards. Since those two forces are not colinear, they result in a torque. Since force #2 is above force #1, that torque acts to rotate the tractor up and over backwards.

The only things that will prevent a backflip are the lack of either enough power or enough traction to complete the job.

xtn

 

[BethesdaEC]

Look at this video. At the start you can clearly see the hitch is well below the axle. Later in the video the front wheels are well off the ground. If the same thing happened at higher speed with bouncing wheels, erratic traction, unpredictable backlash, and other unexpected forces going every which way, then its easy to imagine it could flip all the way.

To me, it somewhat defies logic but see for yourself...

‪John Deere 2 Cylinder Pulling‬‏ - YouTube

The force applied to the ground has no relationship to the axle or where the draw bar is relative to the axle. It is a straight force applied parallel to the ground regardless of wheel size or axle location. The draw bar is a certain distance above the point of force and an opposite force is applied. The only thing keeping these forces in check is the cantilevered weight in front of the point of force (i.e. the front of the tractor).

The draw bar is located below the axle, not because of some magical property that would stop the tractor from flipping, it is just the lowest point and the lower the point, the less rotational force can be applied to the tractor.

The video has all the supporting evidence.

 

[alchemysa]

I thought I could find a video example of an actual flip, but can't so far. However, check this tractor pull video out; Note that the tractor is pulling a wheelie the whole time. Certainly they pull from below the center of rotation, yet still get the front wheels off the ground: ‪NTPA Tractor Pull - Jefferson City, MO‬‏ - YouTube

They're not real big on crowd safety at those tractor pulls are they.

 

[Short Game]

[of course, one should still always pull forwards, from the drawbar and not from some higher fixture ...if you tried to pull a relatively immoveable object backwards from a high FEL attachment point, the rears would come up, no? That is the tractor would count-rotate around the front axle ...that is, until the bucket smacked into the ground]

Well, I tried that once, and the first thing that happened when the weight came off the rear wheels was all kinds of parts in the front drive broke or bent as the situation required (it was quite a loud noise). I did the labor and the 12 pounds of parts from Mitsubishi cost a cool $2,000. (Ring, pinion, sun gear, two bearings, two bevel pinions, all broken, and both axle shafts bent {I straightened these} and assorted seals). I don't try that anymore.