Preventing tractor back flip

[Reg]

I'm of the opinion that the reason you rarely (if ever) see a tractor flip straight over backwards at a tractor pull, it's because the tires are almost almost always spinning, and they usually add enough weight forward of the rear axle to keep the front end about 3 ft off the ground (for best weight transfer).

Now, I also have the opinion that if you have something hooked to the rear of the tractor and it offers enough resistance, be it attached above the axle or below the axle, and with enough torque from the engine, and if one or both of the rear tires suddenly finds traction and stops spinning, that it can and WILL almost certainly flip over backwards. That may be an uncommon sequence of events, but that's why they call them accidents.

I think there are enough deceased tractor operators that would almost certainly bear witness to that, if they could only speak now. That's all I'll say about it.

It doesn't NEED "opinion" - it is simple physics.
In order for the tractor to flip over backwards the point where the draw bar is attached to the chain would have to move FORWARDS.

Under the conditions specified by the O/P that doesn't happen, or at least he didn't ask whether it would flip if/when the chain breaks (-:
I think the attachment point can't get ahead of the rear axle center line - please explain if I am wrong (-:

That attachment point goes lower and lower to the ground as the tractor STARTS to rotate, it approaches the horizontal plane that the tires are on, but an equilibrium is reached before that.

BTW, I was trained to ALWAYS park tractors "nose in" to the wall of the barn.
a) It keeps driving sleet out of the engine compartment.
b) You ALWAYS have to back them out the next morning, which makes for less of a rude awakening if the tires are frozen to the ground.

 

[beppington]

Does hooking up a chain short or long make a difference? Short being as close to the object as possible.

I don't think that matters.

As most realize, pulling from a very high point on the back of the tractor would easily flip the tractor over (in most cases). And the lower you move that point, the harder it'd be ... but never impossible, I don't think, given enough tractor traction & power, & an immovable-enough object being pulled.

 

[ducks13]

In order for the tractor to flip over backwards the point where the draw bar is attached to the chain would have to move FORWARDS.

Under the conditions specified by the O/P that doesn't happen, or at least he didn't ask whether it would flip if/when the chain breaks (-:
I think the attachment point can't get ahead of the rear axle center line - please explain if I am wrong (-:

Reg, you are right, the drawbar won't go forward, the axle will go backwards and the tractor will flip over.

I believe this analysis is a balance of the torques about the axle. If you have a long enough wheelbase (like a dragster) or enough front weight (like a pulling tractor) you will lose traction first or not have enough power to rotate it over. Yes, the distance between the drawbar and the axle also creates a torque about the axle, the lower the drawbar the better. As the front end rises you get less and less anti-flipping torque from front weight until the center of gravity is directly over the rear axle at which point you have no anti-flipping torque from the weight of the tractor. Hopefully before then you've pushed in the clutch, got off the gas or something. Anti-flipping torque, that is my new word for the discussion. :laughing:

 

[bcp]

Pulling from a high hitch:

Why doesn't the tractor in the attachment flip?

Look at the attachment and the movie. Is the driver that good?

YouTube

 

[milkman636]

Nope;
Not even on a cogged track.
Attend a pull some time.
Watch the front end rise, watch the draw bar lower, see the equilibrium.
You will NEVER see a tractor flip STRAIGHT over backwards at a pull.
If one somehow gets off line - that is different and it will be a weird nasty diagonal sort of thing.

Ever notice the lousy tread and amount of wheel spin these guys rely on to keep from flipping? They want the front wheels off the ground so that all the weight is on the rear driving wheels. But they do not those rear wheels to to grip so good that the engine torque that is twisting the axle will flip them over backwards.

If the back wheels grabbed while the engine's full torque was being applied to turning the rear axle, the only thing left that could rotate would be the tractor.

 

[foreman Etexas]

Pulling from a high hitch:

Why doesn't the tractor in the attachment flip?

Look at the attachment and the movie. Is the driver that good?

YouTube

Looks like he keeps working the clutch and bringing the wheels up,and letting the tractor weight coming down to help move the logs.If he didnt clutch it surely he would have went on over.......

 

[Short Game]

If you ask me, this question was settled on page two. If not there, then on page four when he bought the guy a case of beer.

 

[skspurling]

See the simplified diagram below.

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

Bruce

A moves backwards unless you are in reverse.

 

[skspurling]

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

Force 2 acts at the axle. At the ground point, you have the tire lever arm pushing backwards.

 

[skspurling]

Does hooking up a chain short or long make a difference? Short being as close to the object as possible.

I think you are on to something. A lot of times people will use a short chain hoping that the front of whwt they are pulling will lift and not dig in. That changes the direction of the vector the link off the drawbar makes, from pointing along a line below the axle to above it. At that point the front lifts.