Hensley Arrow: How does it REALLY work?

willald wrote:
Look closely again at the video, that shows the range of motion the Hensley goes through.

You're going to notice, that the pivoting/motion it goes through, is NOT the same as the pendulum type motion you're trying to compare it to. ---

Will,

The range of motion shown in the video is much greater than the range of motion which would exist at highway towing speeds. For reference, at a yaw angle of 6 degrees, the rear of a 30' TT would swing about 3' away from straight ahead. In the video, you are seeing yaw angles which are much greater than 6 degrees.

With a pendulum motion, the distance from the pivot point to the trailer remains the same through out. NOT the case with how the Hensley is pivoting here. As the trailer pivots, it moves physically closer to the virtual pivot point. ---

Actually, as the trailer pivots, the virtual pivot point moves closer to the trailer. Remember, when aligned straight ahead, the VPP is about 47" ahead of the ball coupler. At an angle of about 4 degrees, the VPP has moved rearward about 24", and at an angle of about 15 degrees the VPP has moved rearward about 47". Again, for reference, at a yaw angle of 6 degrees, the ball has moved forward about 0.4".

IOW, the trailer is not just pivoting side to side like a pendulum, as it pivots to the side, it is forced to move physically closer to the tow vehicle. Sooo, your comparison to a pendulum motion really is not relevant.

Of course the TT moves physically closer to the TV as it pivots, makes no difference whether the hitch is a HA, a PR, or anything else. When the TV and TT are aligned straight ahead, the HA-coupled TT pivots exactly as though its tongue length has been extended by 47" and it is pivoting about a point which has been moved forward by 47". As the TT pivots, every element of it from the pivot point to the tail lights must move closer to the TV. Makes no difference what kind of hitch you're using. The very nature of pivoting (following an arc) causes a forward movement.

Picture it like a pendulum motion, except that through some physical linkage, as the pendulum swings to the side, the length of the arm is shortened shorter and shorter, the further it swings out. Now picture that same pendulum arrangement in a straight line, with something 'pulling' on the pendulum. As long as there is a force 'pulling' back on the pendulum, it will take a LOT of force to move the pendulum to the side, 'cause you'd have to overcome all the force pulling back, since side-to-side movement results in the pendulum arm shortening? Make sense? This is the arrangement the Hensley is in essence forming.

No, it does not make sense, but let me try to understand it.

Let's say that you and Don have a TT which has a tongue length which can be varied. Don is going to drive down the highway towing the TT and I am going to run along side and try to push the TT to one side. However, you are sitting in the back of the burb and you are able to shorten the tongue length when I try to push the TT sideways.

Lets say the tension in the TT tongue due to wind drag and tire drag is 1000#. If I want to make the TT pivot 1 degree, I need to apply about 17.5# of force.

Now, as I push and the TT begins to swing, you begin to shorten the tongue (move the TT closer to the TV). This does not change the drag on the TT, the drag force still is 1000#. However, lets assume that you are able to shorten the tongue so that the TT accelerates toward the TV at a constant acceleration of 0.2 ft/sec/sec. This would cause the TT to move 0.1' (1.2") closer to the TV in 1 second.

Now, lets assume the TT weighs 6440#, giving it a mass of 200 slugs (love those English units). The additional tongue tension required to accelerate this mass at 0.2 ft/sec/sec is 200x0.2 = 40#. Therefore, the tongue tension now is 1040# and I would have to apply a force of about 18.2#. For comparison, the force exerted on the side of a 30' TT by a 50 mph gust could be about 1500#.

Therefore, I find it difficult to accept the following:

That being the case, its very difficult for any force to make the 'pendulum' swing either direction, since it has to over come the force of the tension/pulling between tow vehicle and trailer. This is why it has the effect of 'locking' the trailer in a straight line, as long as there is resistance/tension between tow vehicle and trailer.

Will

Is there something about the "tension/pulling between tow vehicle and trailer" which I have missed?

Ron