Dual Cam Setup

JBarca wrote:
From mrekim’s thread and other recent hitch head and trunnion bar interaction investigation, I no longer can be sure that the WD chain tension will increase as the WD bar rides up the cam pending what the hitch head is doing. There is a hitch head component to this that is still in the discovery stage.

I agree there's more to be learned about what happens to the WD bar when the TV swings relative to the TT.
And, I thank you for the work you're doing to quantify some of the effect.

However I still have a “belief” that in a compound angle turn when the inside turn WD bar can unload to zero or closer to zero, there is “some” level of increased tension in the outside turn WD bar. How much tension increase is still unknown. Here it the thought path (may be flawed, but this is how I came to it).

I think your current study will go a long way toward eliminating some of the unknowns.

When the TV and TT are on level ground and straight ahead, both WD bars have very close to equal loads. Those WD loads came from the setup of the WD hitch. As a result of this, both left and right WD chain loads are close to the same and the trailer A frame is close to being equally loaded both left and right. So far so good and I think we all agree on this.

Yes, I completely agree.

Now enter the compound angle turn. When the hitch head rolled and unloaded the inside turn WD bar to zero or near zero, there is only the outside turn bar left to provide any level of WD. If the outside bar load stayed the same, then the truck would of lost 1/2 the WD and the front of the truck would of came up enough the driver “may” feel it. Lighter suspension trucks would fell it more so then stiffer suspension trucks.

For reference, the OP's Excursion rose 0.44" in front and dropped 1.38" in rear with no WD applied.
Using 800# bars, he was able to drop the front 0.31" and raise the rear 0.62".
If the WD bar load were reduced by 50%, the front would go back up about 0.15" and the rear would go back down by about 0.31".
Therefore going from the full WD bar load to 50% bar load would change the slope of the TV by about 0.46" over a distance of 137" corresponding to an angular change of 0.7 degrees.
My point is that reducing the WD bar loading by 50% might not make a noticeable difference in the stance of the TV.

I think if we really want to know how the WD bar loading is affected by different simple or compound angles, we need to come up with a method for directly measuring or calculating the load on a WD bar.

I do compound angle turns all the time, and in none of my trucks, 1/2, 3/4 or 1 ton I do not recall the front end going extremely light. We know the WD bar is riding up the cam and we know the rear of the WD bar is rising. We know the trunnion lug on that side is at a down hill angle due to the roll axis. We do not know what the trunnion lug angle in the hitch head did to this equation. That is still an open topic.

I agree. We need to be able to measure the amount of trunnion lug tilt change.
Or, we need to be able to measure the bar load directly or calculate it from curvature measurements.

Since the TT TW did not change, it is still providing a constant force down on the only WD bar that can produce tension. Since the same TW mass is available to only 1 WD bar it comes down to, will the hitch head angle and the rising rear of the WD bar allow an increase in tension?

The tongue weight does not determine how much load is generated by a WD bar.
The load on the bar is a function of height difference between front and rear of bar, slope of the front end of the unloaded bar, and bar stiffness.
The user determines how much load is generated by changing some or all of those parameters.
If you simultaneously raise the rear of a bar and decrease the front slope (e.g. decrease the head tilt), you can have an increase in bar load, no change in load, or a decrease in load.

While the trunnion lug angle in the hitch head may have relieved some of the WD tension, more of the existing TW is available to be held by the outside turn WD bar. An unknown is, did the hitch head angle change enough to not allow more WD bar tension on the outside turn bar and did the rear of the bar riding up the cam over come the loss in the hitch head?

I agree we don't have enough information to answer that question.

The following image shows WD bar curvatures for a TV/TT in three different WD bar loading orientations.
I don't know if the WD bars are the same in all three photos.
If they are the same, we can estimate the relative amounts of bar loading from the relative amounts of bar curvature.
I changed the zoom on the photos to try to keep the vertical scales the same.
As a very rough estimate, I would guess the bar load at bottom left (sharp turn) might be about 15% greater than the load at top left (zero turn).
I see nothing to indicate the load on bottom left is anywhere close to twice the load on top left.
I would expect the bar load at bottom right to be much greater than the load at top left -- maybe twice as much. However, my measurements indicate an increase of about 30%.

In order for the snap up to fail like they do, an increased force presents itself to one side of the WD hitch at the WD chain that overloads a non bolted snapup. A hypothesis is, that the outside WD bar rose enough in tension from the compound angle turn to cause the snap up failure. Now the task is, how to quantify that? If this compound angle turn is not creating the force, then what other combination of actions is?

My current thinking is that the friction force between bar and cam results in an amplification of lift chain tension, and it is that which is causing the problems.
Of course, I always reserve the right to change my mind. :)

Ron