Preventing tractor back flip

[The Haymaker]

23 pages? Really? Enough torque to the axle, enough traction, and it will come up. Yes, lower drawbars should theoretically lessen traction if the nose begins to lift, and yes a longer drawbar will add to that effect plus allow the nose of the tractor to work with more leverage against lift, but if the first two are perfect it will go.

The fix? Run hydrostatic so you can eliminate torque quicker.

 

[Egon]

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

There were three times I've had the front wheels in the air about four feet. Without disengaging the clutch the tractor would surely have gone over. That was when I was a teenager and was invincible.

Had the front wheels of my Kubota off the ground once. That was quickly fixed with a load of rocks in the bucket.


Back when were not many of the racing boats powered by Allison engines. I saw some racing once in Idaho or Montana back in the 60's.

 

[LD1]

There were three times I've had the front wheels in the air about four feet. Without disengaging the clutch the tractor would surely have gone over. That was when I was a teenager and was invincible.

THat is the point. The wheels WILL come up. But if properly hitched, it wont go on over unless you were jerking on it or had a heck of a running start. More than likely, If you would have stayed on it, you whould have reached the point where either

1. the object breaks free and starts moving, resulting in the front comming back down,

or 2. you would have lost traction and the front would have came down as well

 

[johnrex62]

Tmajor started another thread and included a document from Professor Dennis J Murphy who is a professor of Agricultural Engineering. Professor Murphy states definitively in his article that tractors will NOT flip when properly attached to a drawbar.

"When the front end of the tractor lifts, the rear
drawbar of the tractor will lower. This is a function of
tractor geometry. The higher the front end raises, the lower
the rear drawbar is driven. As the drawbar lowers, the
殿ngle of pull and the leverage the load has to tip a tractor
rearward is also lowered. By design, a load will always
lose its ability to tip a tractor rearward before the tractorç—´
CG reaches the rear stability baseline. As the load loses its
ability to continue to tip the tractor rearward, the front end
falls back to the ground. If the tractor operator doesn稚 stop
the pulling action, the entire process will repeat itself,
resulting in a bouncing of the tractorç—´ front end."

His illustrations indicate that he references a chassis attached drawbar and not a 3pt attached drawbar.

There you go folks! It is in writing and available on the internet both! Boo-Yeah! :laughing:

 

[johnrex62]

I was having a discussion with a friend.
Situation - a chain is attached from the bottom drawbar (several inches below the center of rotation) to an immovable object.
My contention is the front wheels are being driven into the ground. Hence, no wheelie. He says it will still wheelie the same as having the pull point several inches above the center of rotation.
Pull above the center of rotation is a no-brainer -you're going over.
Who's right?

This was the orginal question and it was not specifically about flip, but rather about front end wheelie. Sorry, retiredmgn, it will wheelie but you are right that it will only flip if attached above the drawbar.

 

[tmajor]

Tmajor started another thread and included a document from Professor Dennis J Murphy who is a professor of Agricultural Engineering. Professor Murphy states definitively in his article that tractors will NOT flip when properly attached to a drawbar.:

I believe, he may have qualified that statement, by saying the situation was somewhat different on an incline, as the tractor's CG was closer to the rear stability baseline.

 

[johnrex62]

I believe, he may have qualified that statement, by saying the situation was somewhat different on an incline, as the tractor's CG was closer to the rear stability baseline.

He only qualified it for a specific scenario, moving uphill too quickly when the load digs generating a swift change in load momentum. The inclusion of the "too fast" condition kinda violates the safe operation principal and introduces operator error into the equation.

"It is also possible to flip a tractor
rearward when the load is properly hitched to the drawbar.
This may happen when several factors occur. If the
tractor is headed up an incline at too fast a speed and the
load, such as a large log, suddenly digs into the ground, the
rearward pull may be so quick and strong that the momentum
generated by the rearward lift may result in a rear overturn."

 

[LD1]

Tmajor started another thread and included a document from Professor Dennis J Murphy who is a professor of Agricultural Engineering. Professor Murphy states definitively in his article that tractors will NOT flip when properly attached to a drawbar.

"When the front end of the tractor lifts, the rear
drawbar of the tractor will lower. This is a function of
tractor geometry. The higher the front end raises, the lower
the rear drawbar is driven. As the drawbar lowers, the
殿ngle of pull and the leverage the load has to tip a tractor
rearward is also lowered. By design, a load will always
lose its ability to tip a tractor rearward before the tractor痴
CG reaches the rear stability baseline. As the load loses its
ability to continue to tip the tractor rearward, the front end
falls back to the ground. If the tractor operator doesn稚 stop
the pulling action, the entire process will repeat itself,
resulting in a bouncing of the tractor痴 front end."

His illustrations indicate that he references a chassis attached drawbar and not a 3pt attached drawbar.

There you go folks! It is in writing and available on the internet both! Boo-Yeah! :laughing:

He only qualified it for a specific scenario, moving uphill too quickly when the load digs generating a swift change in load momentum. The inclusion of the "too fast" condition kinda violates the safe operation principal and introduces operator error into the equation.

"It is also possible to flip a tractor
rearward when the load is properly hitched to the drawbar.
This may happen when several factors occur. If the
tractor is headed up an incline at too fast a speed and the
load, such as a large log, suddenly digs into the ground, the
rearward pull may be so quick and strong that the momentum
generated by the rearward lift may result in a rear overturn."

Sound exactally like what I have been preaching. Do you have a link?

 

[tmajor]

The post with link is here.

 

[xtn]

"As the drawbar lowers, the
angle of pull and the leverage the load has to tip a tractor
rearward is also lowered. By design, a load will always
lose its ability to tip a tractor rearwards."

The dear professor generalizes. The load's ability to tip the tractor rearward does NOT drop all the way to zero in every possible geometry. There is a pretty good range of connection angles and drawbar positions that have that tendency drop pretty low, but always remain positive.

Now there may be no real world tractors that can force the issue with enough power and traction to flip themselves under level and steady conditions. And that's fine; I've not argued that. But it is not accurate to imply that the load's ability to tip the tractor always reaches zero at some point.

LD1 you have me confused. Did you not tell me you think the tires and axles cannot move rearwards? And don't you agree that the geometry requires them to move backwards if the nose comes up? So you must then believe that there is a locked condition in which the tires must spin, the engine must die, or something must fail.

But now I've seen you mention the fact that the nose DOES start to go up. Then by geometric necessity you must agree the rear tires and axles do start to move backwards.

xtn

PS - I just checked my own little tractor, and found that the drawbar sticks 8" out past the tires. Guess I'm relatively safe.