Hensley Arrow: How does it REALLY work?

Welcome to the discussion, Dave. As far as your "straight truck" theory, you might want to re-read some of the posts by Ron and I. Are you sure you caught this one (quoted below)?

tluxon wrote:
I completely agree with Ron's assessments so far.

I'd like to address this impression of "rigidity" in the Hensley hitch. I'm guessing that most Hensley owners at one time or another have seen the marketing video that has the hitch model segment I posted captures from back on this page. The first time I saw that video four or five years ago, I also had the impression that lateral forces acting on the trailer wouldn't create a bend at the hinge, while turning inputs from the tow vehicle would readily bend the same hinge. That same impression I had seems to be held by just about anybody who's ever towed with a Hensley or seen the video. However, whether intentional or not, the test model shown is deceiving in that it misrepresents the actual geometry involved.

To follow what I'm talking about, please take another look at the test model.



Pay particular attention to where the "wheels" are on both the pretend TT and the pretend TV. Do you notice how much closer the TV's rear axle is to the hitch than you'd see on a real TV. Considering the projected VPP of the Hensley being some 47 inches forward of it, the VPP on this model is considerably forward of the rear axle, which requires that the reactionary moment of the TV be exactly opposite of what the most common reality would be. Not only does this make it impossible to bend the hitch when applying lateral force to the TT, but based on the moment the VPP is putting on the TV, would cause the TV to try to bend the hitch the OPPOSITE direction!!!

Now, take a look at where the TT's axle is. This model places the theoretical TT's axle much, much closer to the hitch than would ever happen in reality. This serves to give an extremely short lever to the lateral force applied, which limits the resulting moment about the TT's axle to a scant fraction of what would happen under real conditions.

I hope that by describing these characteristics in the Hensley test model, you can see how it is possible that ALL the lateral forces applied are reacted to by the wheels and NOT by the linkage of the hitch itself.

So, if you follow my reasoning here, you'll agree that there really isn't anything magical about the linkage in the hitch other than how it projects the actual pivot point forward.

I'd like to point out that the 4-bar linkage can only act like a rigid "box" when both vehicles are perfectly aligned and there is no translated lateral force.