Hill Climbing Primer

[Raised on a Deere]

Some will be confused, some will not

It's a complicated subject ;-)

If it is so complicated why did us farm boys back in the sticks and hills of Kentucky know enough to lengthen the drawbar enough so that by the time the front end was getting very far off the ground the drawbar end was getting close enough to the ground so as to be creating less of a tipping force. Pulling at ground level there is no tipping force generated by a tractor in pulling against its load.

But I do remember some of the same dimwitted discussions (at least they seemed that way to my 12 year old mind) going on where in the face of proof time after time that the front end would come up just so high with the longer drawbar, because they could not figure out why they would try to prove that the drawbar length had nothing to do with how much the tractor reared up as we called it. Even when they flipped their tractors they allowed it was for some other reason than the short or high draw bar. One day I got the idea of hitching some thing to the top link area of a tractor and dared the man to try to pull my dads tractor. He was fool enough to try and after that he did not like me at all. I wished I had never brought it up.

The whole discussion got so meaningless I quit even suggesting that someone lengthen their draw bar when we would wind up in some sort of pulling situation among the neighbors in getting a downed tree out of the way or pulling a coal truck out of a stuck situation. Saw many a time where the tractor stood on its back end and the operator had to jump off. A friend got killed due to a back flip.

My current tractors do not even have the setup to lengthen or shorten the draw bar but before everything became 3pt they all had that set up. Some of the manuals even suggested lengthening the drawbar to protect against a surprise back flip, John Deere Model A to mention one.. Come to think or it that is how us ignorant folks knew about it I guess. Some of us could read:drink:

 

[CalG]

If it is so complicated why did us farm boys back in the sticks and hills of Kentucky know enough to lengthen the drawbar enough so that by the time the front end was getting very far off the ground the drawbar end was getting close enough to the ground so as to be creating less of a tipping force. Pulling at ground level there is no tipping force generated by a tractor in pulling against its load.

But I do remember some of the same dimwitted discussions (at least they seemed that way to my 12 year old mind) going on where in the face of proof time after time that the front end would come up just so high with the longer drawbar, because they could not figure out why they would try to prove that the drawbar length had nothing to do with how much the tractor reared up as we called it. Even when they flipped their tractors they allowed it was for some other reason than the short or high draw bar. One day I got the idea of hitching some thing to the top link area of a tractor and dared the man to try to pull my dads tractor. He was fool enough to try and after that he did not like me at all. I wished I had never brought it up.

The whole discussion got so meaningless I quit even suggesting that someone lengthen their draw bar when we would wind up in some sort of pulling situation among the neighbors in getting a downed tree out of the way or pulling a coal truck out of a stuck situation. Saw many a time where the tractor stood on its back end and the operator had to jump off. A friend got killed due to a back flip.

My current tractors do not even have the setup to lengthen or shorten the draw bar but before everything became 3pt they all had that set up. Some of the manuals even suggested lengthening the drawbar to protect against a surprise back flip, John Deere Model A to mention one.. Come to think or it that is how us ignorant folks knew about it I guess. Some of us could read:drink:

I'm not sure if your comment was directed at me, but if you have read through these many posts in this thread you will find that my statements here agree with all that you have written.

As posted, "some will be confused, some will not". Your experience speaks clearly

 

[Egon]

Some will be confused, some will not

It's a complicated subject ;-)

Some are confused, others are not. Others just may understand what is going on. Right eh.

 

[SPYDERLK]

Absent acceleration the only effect to tip the tractor comes from the force it exerts rearward on the ground. This acts thru the lever equal to the tire radius -- the axle to ground distance ... the drive lever. Any resistance to tractor motion applied below the axle has a countering effect on the ability of the drive lever to tip the tractor. A tractor drawbar is not low enuf to fully counter this. -- We wouldnt like it if it did, because it would prevent weight transfer to the main drive wheels. We want to have a good bit of weight transfer to the rear for traction. ... So the drawbar is carefully placed an appropriate distance below the axle to provide this transfer. Good if its not too much for safety. ... So the thinking designer manipulates the drawbar length extending behind the axle factored against its height so that the backtip providing weight transfer is moderated due to a simultaneous progressive lowering of the pullpoint. Physics can be analogous to free money to the attentive designer. ... Still, this passive system has its limitations. >The drawbar must extend back beyond the tire circle for best effect. Some do some dont. It depends on 3pt arm length and placement. A long drawbar may interfere - or may be set short for one function and not lengthened for an aggressive pull. For an aggressive pull you want a long drawbar so that the end comes to ground early enuf in tip cancelling the drive lever soon enuf to fully protect against inadvertent very aggressive traction or drive lever changes ... [think a sudden hook up where the tractor rips itself out of the hole youve dug trying to pull. Force points are shifting and the momentum of a quick tip may not be possible to arrest.
.....As far as the dragster quote: Compare and contrast highly accelerative conditions with a steady state pull. Weight distribution considerations will receive extra credit.

The tires interact with the ground. The pullpiont also interacts with the ground. Its effect is governed by its position [^ v < >] wrt the axle. The gears acting and reacting thru everything in the chassis give you a torque output onto the pivot of the drive lever - axle. This yields a rearward force on the ground from the end of the lever in inverse proportion to the levers length. If theres no resistance theres ~no torque. The tractor just glides ahead. With resistance comes torque. Depending on where that resistance is applied to the chassis the tip torque on the chassis can be either proportionally increased or offset. A pullpoint between axle and ground offsets ... and at ground level fully cancels tip.

... Whats the pull point of a dragster?
larry

You cannot tip the tractor backwards by pulling at any level between the ground and the midline of the axle for the following reason: there will never be enough traction for the rear tires.

Your last few words is the point of contention. There are those that say it can NEVER tip over backwards even if the rear tires maintain traction. You last comment is the truth. The tractor will lose traction and thus not tip over backwards. Depending on application you may experience a loss of control momentarily, but no tip over backwards.

Oh. ... WHO ARE THOSE THAT SAY THAT?

 

[Raised on a Deere]

I'm not sure if your comment was directed at me, but if you have read through these many posts in this thread you will find that my statements here agree with all that you have written.

As posted, "some will be confused, some will not". Your experience speaks clearly

I was not directing at anyone, just venting my frustration at how such a simple thing can get so muddled when we try to explain it. After all, it is as plain as the nose on my face I feel sorry for someone looking for a quick handle on dealing with this subject who runs across this thread. Actually it could be a blessing if it challenges him to dig in and sort all that has been said. That would take more patience than most who would be looking here for answers to such a question as being discussed.

Really not directing at anyone. I am just amazed that this thread has continued so long. Sharing my experience of this being common barnyard lore since tractors began. As a four year old I remember my grand dad having a discussion with a neighbor on how to hook a Fordson steel wheeled tractor to a stump and they stood there arguing about it. I couldn't understand why my grandfather was getting so ugly. Then in 1950 (I was 12) when Dad bought the John Deere A (biggest day of my life I thought) the dealer was explaining about the drawbar length setting and how it was John Deeres special solution for safety (they made it convenient to change the length) and how they were a leader in the field. The drawbar length thing caught my ear and I spent a lot of my tractor time observing how the tractor behaved at various lengths. With a light front end tractor it was easy to detect differences in the steering. I went on to a career as a mechanical/electrical engineer largely because I had gotten in the habit of trying to understand what was going on in all those arguments ( discussions) among the farmer neighbors. Remind me to tell you sometime about a discussion about electricity.

Please no one take an insult. I am still amazed that this thread has continued so long though. I suppose if one wanted to do a little study on how to make this person or that person look like a blooming idiot this thread could go on until a nuclear holocaust. Of course no one is being an idiot but on this subject people listening might think it looks so.

 

[sacmarata]

I never knew the whole thing was worth discussing but have heard some of the same silly arguments.
I couldnt believe it when I saw 27 pages to a subject that simply explains itself when applied.
I guess thats why we have applied sciences and theoretical sciences...lol...applied science makes things happen while theoretical science watches and scratches its butt saying "it cant be!"

 

[CalG]

Yes 27 pages

Testimony to the depth of confusion that has rooted it's self through casual observation.

But worth discussion? I would say so! People have lost their lives over these vary details! One fellow recently less than 5 miles from my home. An life long farmer, pulling the wood wagon. Sad.

By "practical science" do you include Darwinian? Misinterpretation assure the experiment is not repeated? ;-)

To boil it down, For me, if the rigid draw bar (NOT A THREE POINT TOOL BAR!) extands out past the tire radius, and is at "normal" hitching height (well below the axle).
I am confident that the tractor will Not go over backwards if the load hangs up. At least on level ground. Up hills? , I'm keeping a foot on the clutch pedal ;-)

I would like to Test my draw bar, to confirm that it will not fold under these extreme conditions, But I doubt I will, trusting the depth of steel that is there.

This thread is "a Hill climbing primer" but didn't get into the phy-sicks of hill climbing. I doubt there are many that would stick out a discussion over that branch of tractor stability.
May as well bring up the relative stability of tricycle vs wide front ends ;-)

 

[sacmarata]

ahhhh... Darwinian evolution. Now theres a topic that can run hundreds of pages long with both sides feeling like they murdered the other. Maybe I should start a thread titled "Punctuated equillibrium of Korean tractor design." For the sake of all those involved here, I'll hold my opinions.

That is unless we can get into a nice conversation about radio isotope dating and get away with it

 

[JWR]

ahhhh... Darwinian evolution. Now theres a topic that can run hundreds of pages long with both sides feeling like they murdered the other. Maybe I should start a thread titled "Punctuated equillibrium of Korean tractor design." For the sake of all those involved here, I'll hold my opinions.

That is unless we can get into a nice conversation about radio isotope dating and get away with it

Hey ! Back off ! I think I dated a radio isotope once ...

 

[k0ua]

Hey ! Back off ! I think I dated a radio isotope once ...

Yeah, and she glowed in the dark... which come to think of it was kinda handy:laughing: