Hensley Arrow: How does it REALLY work?

tluxon wrote:
I agree with you Ron, but I believe it's clear that combining the "pendulum" characteristics of the HA with a TV-TT tension provides more straightening help than what you get with a conventional hitch. And we all know that a trailer can be straightened up pretty quick behind a conventional hitch by engaging the TT brakes with the brake controller.

Tim,

I agree 100% with the "more". But, our primary consideration should be, how much more. It is only by quantifying our findings that we can produce meaningful results. Your values for trans-rotation were a good step. However, we need to be aware that an 8-degree swing will cause the rear of a 30' TT to move to the side about 5'. If we want to study how the HA might resist the onset of TT swing, as opposed to how it might resist it after it gets to 8 degrees, then we should be looking at what happens with a swing of one or two degrees.

To try to put these HA trans-rotation and "reel-in" effects into perspective, let's consider the following:
Assume a 30'-long HA-equipped TT with 6000# on the TT axles.
Assume a 50 mph wind gust produces a right-directed side force of 1500# on the TT.
Assume a "drag/pulling" force of 1000# (probably more like 500#) .
Assume the TT tires produce a lateral force of 600# per degree of swing (references can be provided).

To simplify calculations, let's initially assume that the wind force is resisted entirely by tire forces and then correct for the estimated HA effect at that angle. With tire lateral resistance alone, the swing angle would be 1500# / 600# per degree = 2.5 degrees.

At a swing of 2.5 degrees, the HA's ball would move about 2.1" sideways and 0.5" forward. The HA's VPP would be about 16" left and 40" forward of the "straight-ahead" ball position.

With a conventional hitch, the "swing resistance" resulting from the "drag/pulling" force effect would be about 50# at the TT's axles. With a HA, the "swing resistance" would be about 60# at the axles. The HA's "reel-in" effect might increase the tongue tension by about 20# which corresponds to an added "swing resistance" of about 1.2# at the axles.

These assumptions suggest that the conventional hitch "swing resistance" would be about 50# and the HA's "swing resistance" would be about 61#. The HA's "reel-in" effect would be about 1.6% of the total HA effect.

Now, if we add the HA's "swing resistance" of 61# to the tires' resistance of 1500#, we have a total resistance of 1561# which is greater than the wind force. The tires need to provide only 1500-61 = 1439# of resistance. This means the swing angle would be reduced to 1439 / 600 = 2.4 degrees versus the assumed 2.5 degrees. However, reducing the swing angle by 0.1 degree would have negligible effect on the hitch-related "swing resistances".

So, we can summarize as follows:

Lateral wind force = 1500# (100%)

Lateral tire force = 1439# (95.93%)
Conventional hitch resistance = 50# (3.33%)
HA drag/pull added resistance = 10# (0.67%)
HA "reel-in" added resistance = 1# (0.07%)

I welcome any suggestions for other methodologies and assumptions for analyzing this problem. But, for the time being, I'll stand by my belief that it is the tire lateral force, not the hitch (HA or otherwise), which controls the swing.

Ron