Hensley Arrow: How does it REALLY work?

BurbMan wrote:
Picture a pendulum with a rubber band connected to its bottom and the other end fastened to the ground surface below the pendulum. Any attempt to start the pendulum swaying along its arc will be resisted and eventually stopped by the force the rubber band exerts. The rubber band will effectively dampen the movement until the pendulum is once again hanging in a static position.

Don,

I'm glad that you did not contend that the rubber band would "lock" the pendulum at the center position and that no amount of force would be able to move it to the side. The tension in the rubber band would cause an increase in the amount of force required to move the pendulum. For example, if the tension were 1000#, it require an additional 17.5# of force to pivot the pendulum 1 degree.

However, the tension in the rubber band does not dampen the motion of the pendulum. The motion is damped only if there is an energy dissipating device, such as a shock absorber, in the system. That's why cars have shocks. A coil spring (or a rubber band) does not have enough internal friction to provide any significant damping.

Once the displaced pendulum is released, the rubber band tension will add a restoring force which will make the pendulum accelerate faster toward the center position. Energy will be conserved and the pendulum will swing to 1 degree in the opposite direction. Eventually, friction at the pivot point plus the small amount of internal friction in the rubber band will still the motion; but it is not due to the tension in the rubber band. Your use of the term, "eventually stopped", is correct; but not for the reason you postulate.

What Will and I are saying is that the drag and wind resistance created by the trailer act just like the rubber band in my example. Traveling at hiway speed, these forces amount to the equivalent of a very thick rubber band on the bottom of that pendulum, so any attempt to swing the pendulum is quickly dampened by the rubber band.

First - a rubber band (or a steel spring) would not add any appreciable damping.
Second - the tension in a rubber band will increase as the rubber band elongates. In your HA theory, are you claiming that the drag and wind resistance increase appreciably as the TT moves a fraction of an inch closer to the TV? If not, how does the rubber band analogy enter in?

Yes, the math says that movement is allowed, but you are ignoring the fact that the HA relies on tension bewteen the TV and TT to resist any movement introduced into the 4-bar linkage by the TT.

You have used the phrase, "resist any movement". If by this you mean, "absolutely lock out any movement", then I do not agree. If you mean resist in the sense that the mass of a pendulum resists its being displaced from its center position, then I do agree.

AND, it's not a question of whether the TT is allowed to pivot...as an example, if I am driving on the interstate at 70 mph with the HA connected to my 34' TT, and a 50 mph gust of wind comes up perpendicular to the trailer, I will feel the TT move. HOWEVER, the HA effectively dampens this movement to a single push, and this tension that Will and I are trying to explain prevents that intial movement from repeating itself into a sway condition, as a pendulum would when dropped from a point along its arc.

It is not the HA which is damping the movement. It primarily is the lateral resistance provided by the TT' tires which does the damping. Energy frequency content of a gust of wind is not sufficient to cause sustained oscillation in the presence of normal tire damping.

The reason that conventionally-coupled trailers tend to sway under these conditions is that some of the lateral wind load on the TT gets applied to the rear of the TV via the ball coupler. The TT tends to steer the TV and the driver might over compensate which can contribute to sustained oscillation of the TT. With the HA, the tendency for the TT to steer the TV is significantly reduced primarily due to the forward relocation of the pivot point.

I fail to comprehend why some HA owners cannot accept that the HA works for two fairly simple reasons:
1. the HA reduces the magnitude of the lateral loads, and
2. the HA reduces the length of the "steering lever arm".
These two effects combine to significantly reduce the "steering torque" imposed on the TV. This, in itself, is sufficient to explain why HA owners do not experience sway. That's all there is to it. There's no reason to make it more complicated with "lock up" theories, etc.

Ron