Coast Resorts Open Roads Forum: Hensley Arrow: How does it REALLY work?


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Ron Gratz

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Posted: 05/12/05 08:56pm

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Stressor wrote:

The virtual pivot will describe an arc in space on a horizontal plane as the side bars change direction.

Milt,

I fully agree. My AutoCAD models indicate that the loci will approximate an ellipse. Depending on which HA pin spacings you choose to assume, the major axis of the ellipse might be in the range of 47" to 54", and the minor axis will be around 38" meaning the pivot point can be as much as 19" to either side of the TV's centerline.

Ron

Ron Gratz

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Posted: 05/12/05 09:26pm

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Claude B wrote:

We also agree that sway only occur at speed over 45 to 50 mph (+/-)
So, at this speed, TT and TV are in straight line 99% of the time. This is where the HA desing is unique, it locks completely (from the TT point of vue) the TT and TV just like riding on a railroad. It has the same effect as welding a 6" I beam from the back of the TT to the front of the TV. Rotation is impossible if induce by the TT (sway). The HA trapezoïd 4 bars linkage combined with the 2 struts bars are locking the TV and TT. On highways or country roads, the TV and TT are always almost straight so with the HA, there is no apparent pivot point of rotation close, after or forward the TV axles. Lateral forces will be on the entire TV frame (from the HA to the receiver to the TV frame)..

Claude,

I must respectfully disagree with this part of your post.

Yes, the HA does "lock" the TT tongue to the upper (rear) part of the hitch via the struts. In similar manner, the PullRite locks the TT tongue to the hitch via the WD bars. However, both hitches effectively extend the TT's tongue forward to a new pivot point.

With the HA, although the TT is "locked" to the rear part of the hitch, the rear part of the hitch is not "locked" to the front part of the hitch. The linkage allows the rear part to simultaneously rotate and move sideways relative to the front part. Therefore, the TT is not "locked" to the TV.

The key point to remember is that when the TT and TV are aligned nearly straight ahead, the HA and the PullRite act in the same manner except that the pivot points generally are at different distances from the TV's rear axle.

Ron

Ron Gratz

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Posted: 05/12/05 09:49pm

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tluxon wrote:

...Of course, this is using Will's numbers which I believe are only guestimates. We'd have to know the actuals to determine how far up the VPP really is.

Tim,

The numbers stated in the Hensley patent document are:
Front pins 7 1/8" c-c
Rear pins 7 7/8" c-c
Side links 4 1/2" c-c

Using these numbers, I got a distance of 47.1". However, with these dimensions, I was not able to reproduce Hensley's stated maximum turning double angle of 165 degrees.

When I changed the side links to 5" c-c, I got a pivot point distance of 52.4" and was able to reproduce the 165 degree angle.

Ron

Claude B

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Posted: 05/12/05 10:07pm

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Ron,

Did you had the chance of to see the HA promotionnal video ?

I'm talking about the scene where there is the hitch mounted on a demo stand on wheels and the guy showing how it works. This is where I start to figure out why the TT is lock behind the TV in a straight position on the road. Of course, if you try the HA on a very small utility trailer and you are able to lift the trailer by the rear bumper (wheels of the ground), no it's not lock but if you push laterally on the tongue (sway forces) with the wheels on the ground, it is lock.

Claude
2013 Gulf Stream VISA 19ERD
VW Touareg TDI 2013
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Ron Gratz

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Posted: 05/12/05 10:40pm

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tluxon wrote:

I have the Hensley video where they use an actual hitch for demonstration purposes. They show that when the TV tries to create an angle with the TT there is no resistance and the angle is easily created. Then they demonstrate that applying strong lateral forces to the TT side of the hitch results in no angle being created - Yes, the combo moves as a single unit. I don't know that that answers where the pivot point is so well, but it sure addresses the concern with TT induced sway.

Tim,

In a previous thread, I made several postings (running across two pages) offering my opinions on Hensley's "model" TV and TT coupled by a full size HA.

I would appreciate your comments on my remarks since you have seen the video and I have not.

Ron

Ron Gratz

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Posted: 05/12/05 10:42pm

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Claude B,

Please refer to my previous post.

Ron

tluxon

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Posted: 05/13/05 02:45am

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Ron Gratz wrote:

tluxon wrote:

...Clearly, as the angle between the TV and the TT change, the point of intersection between their centerlines changes, and this way we have a name to reference that moving point.
Tim

Tim et al.,

I don't think there is any significance that can be attached to the point of intersection between the centerlines of the TT and the TV.

There's only no significance if you disregard what it looks like to the layman from a birdseye view. I would submit that it is sometimes useful and helpful to provide descriptions to things even though they may not be considered "significant" for calculations or for understanding the primary interactions.

Ron Gratz wrote:

tluxon wrote:

You have a remarkable understanding of how the Hensley works considering that you haven't even seen the video. In the demonstration on the video, the guy only pushes laterally on the front of the TT tongue portion of the model. The only other thing he does is go to the front of the TV portion of the model and rotates it to simulate the TV turning the TT. I have snapshots that I just took off of a video capture that I'll post on here next.

Tim -
wife Beverly & 2 boys who love camping
2002 K2500 Suburban 8.1L 4.10 Prodigy
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Replaced 2000 Sunnybrook 26FK on 8/6/04

tluxon

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Posted: 05/13/05 02:51am

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Here are captures from the Hensley video where the demonstration model is manipulated. In the first two images, the "hinge" did not bend or move at all.

[image]

This should help.

Tim

Ron Gratz

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Posted: 05/13/05 06:19am

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Tim,

Thanks for posting the "test model" images. They pretty much confirm what others have explained to me verbally.

I suggest that anyone who is trying to interpret the significance of this "demonstration" should keep in mind that the probable pivot point for the "model" is out in front of the "TV" and not 20" or so behind the rear axle as it would be with an actual TV.

Can you tell from the video if any or all of the wheels are caster wheels? Is the front wheel of the "TV" always at 90 degrees?

Ron