Pull from the front or the rear?

[bcp]

On the 8N, I don't see any sign of a low drawbar. I looks like it was hooked high.



Bruce

 

[3Lfarms]

I paused that video there too. I don’t know much about those old Fords, but it looks like there is a spot for a swinging drawbar, but nothing there.

 

[Reb954]

I think the FBI should investigate this roll over phenomenon.

 

[rScotty]

Does that analysis include the torque that the pinion gear is exerting against the ring gear?

I believe that it does. The pinion reaction is added to the weight and distance moment part of the overturning moment for the CG of the tractor; that of the ring gear is added to the forces at the interface of of the tire with the ground.

There are always problems when you go from a static to a dynamic analysis, because every time any component reaches a limit everything changes.

Basically I believe we can describe the problem this way:
If the drawbar is above the point where the tire touches the ground, the potential for overturning exists. After that, it's just a matter of how much force we need to make it happen.
rScotty.

 

[RoyJackson]

How does a drawbar rise up above the rear axle when itç—´ mounted below the differential

Andy

I think some of the posters are confusing the tractor's drawbar with one that's mounted on the 3PH.
A tractor mounted (below the rear axle) drawbar will tend to pull the front end of the tractor down....much less likely to result in a rear rollover

 

[RoyJackson]

Good question. Towed implements get towed from the drawbar, and 3pt implements get attached to the two lift arms and top-link. I never found a use for the 3 point drawbar when I had a machine with a 3pt hitch.

I have towed a trailer using a 3PH drawbar...looks something like this:



Used it to tow a smaller trailer (probably a quarter ton) when we lived in Pennsylvania.
Nice trailer, and I've regretted leaving it in PA.

Anyway, a drawbar such as shown in the picture works great for trailers, but if I was towing or pulling something without wheels, I'd use the tractor mounted drawbar most tractors have below the rear axle.

 

[goeduck]

I think some of the posters are confusing the tractor's drawbar with one that's mounted on the 3PH.
A tractor mounted (below the rear axle) drawbar will tend to pull the front end of the tractor down....much less likely to result in a rear rollover

Exactly. Which is why tractor pull tractors do not flip over (that 8n was hitched high). The front tires bob on and off of the ground.

 

[California]

If the drawbar is above the point where the tire touches the ground, the potential for overturning exists.

That's how I visualize it.

But then I wonder if the tractor is standing vertical, drawbar just touches ground, and the driveline still applying torque, what happens?

 

[RoyJackson]

That's how I visualize it.

Maybe...but you're not correct...
Visualize a pull from a point directly below the rear axle (that is, a tractor mounter drawbar). Pulling a heavy load from below the axle will tend to counteract any tendency to lift the front end.

 

[MossRoad]

Basic physics - even known when I got my engineering degree and available through every states dept of agriculture. Modify your tractor so the coefficient of traction approaches infinity and it痴 going to flip backward. The diagram I posted is from a basic tractor engineering book. Pivot point is bottom of rear tires. Multiply force times lever arm to get the opposing moments. Pull times pull height is opposed by mass at CG times lever arm. If the traction is poor the pull cannot reach the point where the front end will lift. If the traction is high the front end will lift, just like shown in all these tractor pull pictures. Same thing in the picture I知 sure everyone has seen of the driver who chained logs to his wheel. Every time a log hit the ground the tractor front raised.

Is the pivot point the bottom of the rear tires? Everyone thinks its the center of the wheels where it connects to the hub.

Pivot Point is defined as the center point of any rotational system.