Hensley Arrow: How does it REALLY work?

bettered wrote:
That's sort of the problem. It's very difficult to discern exactly what's happening with the side links because you can almost never see them. I was running my hitch back and forth and trying to determine exactly what the links were doing when I concluded that they (being shorter than the distance between the bearings) can and do fold over each other (the lines of action cross) during the last (tightest) part of the turn. That's what gives the hitch the 165 degrees of travel.

Clearly the front and rear bars overlap at this point, but it's the action of the side links "meshing" that makes it possible.

Ed

Unless some of the links extend considerably beyond the points at which they're pinned, I don't believe the side links can ever cross over each other, or "mesh" as you say. To help illustrate my point, I put together a sketch in AutoCAD and that shows a progression of the linkage positions in different colors as the rear bar rotates clockwise. Very shortly after the furthest rotation shown is when the side bar lengths limit any further rotation.

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NOTE - This image in incorrect - I'll be replacing it shortly
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Does that help?

BurbMan wrote:
...I think we pretty much beat the concept of the 4-bar linkage to death. I'll go out on a limb and say that we all agree that the creation of the VPP by the linkage is the cornerstone of the HA design and largely responsible for its effectiveness. Recent conversation has largely been focused around the specifics/details of this.

I was hoping we wouldn't have to linger quite so long on the concept of the 4-bar linkage either, but understanding it was at the core of the answer to the original post. There was more resistance to some aspects of the linkage than I expected to find, but it took a while to figure out the nature of the resistance and what kind of information would best clear it up. That path ended up taking a few side-trails and a fair amount of interest kept it going perhaps longer than was best for captivating everyone's interest.

BurbMan wrote:
We did start to touch on a secondary component of the hitch, a point that you brought up Tim, about the HA's ability to reduce lateral forces on the TV based on the moments created by the 4-bar linkage. I think we got off track before we sufficiently quantified that concept.

All we need now is a little differential calculus to show that the 4-bar linkage not only changes the force moments, but also affects that rate at which those forces build on the TV in response to forces applied to the TT. (dv/dt=?)

I agree that there is more good stuff to delve into regarding lateral forces, resultant moments, and the various reactions required. I think we might lose a few people if we try to find problems that require differential equations to solve, but I believe there are plenty of real-life scenarios that would be quite interesting to look into and quantify that wouldn't require differential equations to solve. In fact, I was considering making a type of spreadsheet where people could plug in the known values for their particular setup, and it would show the leverage advantage that a Hensley would give them.

BurbMan wrote:
I would also suggest that we could summarize for the Les the Moderator the relevant posts to keep in the thread and condense to a sticky.

Les is already helping me get started in that direction. It may involve creating a new cleaned-up post/thread that links to this one for those who want all the skinny.

Tim