Hensley Arrow: How does it REALLY work?

Stressor wrote:
I like that Tim. The Hensley may not be a 4-bar linkage, it may only be a 2-bar linkage, in that only 2 bars can move. Your demonstration allows the upper and lower bars to pivot freely, but on the hitch, this is not allowed by virtue of a lot of steel, and the geometry of the links.

No, all 4 bars are allowed to move freely on this hitch. The only thing that makes you think the top and bottom bars aren't moving is the fact that they're fastened securely to a relatively mammoth TT and TV and both of those vehicles are very well connected to the ground via gravity and the friction in their tires.

Stressor wrote:
A more appropriate demonstration would occur if you grasped the top bar, (TV), in your left hand, and the bottom bar, (TT), in your right hand, and then, pulling outward with both hands, tried to turn the ends of either one in towards the other. If the geometry is correct, only the bar with the shortest distance between the pivot points will allow a "Turn" to occur.

No, this would not be appropriate for isolating the behavior of the hitch from the contribution of the ancillary vehicles and their intimate connection with the ground. If anything, your method would come closer to demonstrating the behavior of the entire system, which I was hoping to avoid in this elementary step.

Stressor wrote:
Reversing the hitch is easier than one would think, just put the TV in reverse and watch what happens to the trailer as the steering wheels are turned and the forces are reversed.

Sorry, but that would not be a good way to see what happens when reversing the hitch alone unless you have a very unique trailer that has a long wheelbase and wheels on the far side from the hitch that turn. The fact that most trailers don't have an engine and driveline to pull with is an added difficulty.

The bottom line is that I think you're going to have trouble understanding the contribution of the hitch ALONE unless you are able to totally blank out your experience of observing the behavior of the whole system with at least one vehicle attached. That changes EVERYTHING because of the all the translations that the 4-bar linkage requires.

I can't continue to invest this much time trying to explain a relatively simple concept, so if you're going to insist on disagreeing with me I'll just have to let you have the last word and trust that impartial observers will be able to discern for themselves what they want to understand. I was hoping to eventually drop in a free body diagram focused at the hitch, but without a basic agreement on the nature of the linkage (such as what is free to move and rotate and what is not - WITHOUT anything attached), it would serve little purpose.

Let me ask you this. Would you believe a Hensley engineer if he confirmed that there was nothing built into the linkage that prevents any of the 4 bars from translating? I can try to work from that angle if you think it would make a difference.

Thanks,

Tim