tluxon
Kirkland, WA
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Stressor wrote:It is totally predictable that if there is a slight wiggle from the TV, there will be a slight wiggle observed in the TT. The hitch is simply working as designed, according to simple mechanical principles. I'm glad you mentioned "simple mechanical principles". The concept of a linkage that is free to pivot from one end but locked from the other is the least simple mechanical principle in this entire thread. How do you explain the video Dave made that I linked a couple posts back? The orange part of the hitch sure doesn't look very "locked" to me. Anybody else think that looks locked?
Stressor wrote:No scientist ignores data in favor of speculation. There are many many unsupported hypotheses here, none of which are demonstratable, falsifiable, and many of which ignore published information, and for that matter, video tape of the hitch in operation. I apologize - I didn't realize you considered yourself a scientist. Perhaps I'm not following you because it looks to me like you're implying that published information can be considered as "data". I don't understand the soundness of that reasoning.
Tim
Tim -
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willald
NC
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Ummm....maybe its my imagination, but it seems this thread has divided into two major, separate debates:
1. Stressor vs. everyone else, in the argument of whether or not the Hensley is physically and completely locked, from the trailer end (with Stressor's now famous photos, showing the cable attached to the side of the Hensley)
2. Burbman, myself vs. Ron Gratz and Tluxon, in the argument of whether or not the hensley forms somewhat of a 'virtual' lock from the trailer end, when being pulled on/tensioned. No, its not a complete 100% lock, but due to the forces involved, its pretty close to such.
No disrespect intended toward Stressor or anyone else, but I think argument/debate #1 is not going anywhere, and is generating a few almost 'hateful' remarks, which is not good.
Argument #2 OTOH, is something I think we can prove/disprove (or at least discuss more peacefully). And, if we do prove this assertion is true, I think it will satisfy Stressor also, that the point he's making is true also, in a round-about way. IOW, this would make us all happy, and in agreement. ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/smile.gif "smile")
That being the case, I would like to respectfully request that we concentrate on #2. I think that might be a bit more productive..
Will
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TeryT
Scottsdale AZ
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42 pages of this!!?? Oh my gosh! Please next concentrate on how many angels really can dance on the head of the pin! LOL And I've been accused of being an over-analytical!
OK, I've been gone for awhile (enjoying my Hensley) and haven't the time/inclination to read all 42 pages here, but I am curious - where's "Stressor's now famous photos"?
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TeryT
Scottsdale AZ
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Alright, I found the photos, and understand the basic arguments. (although the angels on the pin head would still be an interesting discussion)
1. Has anyone tried putting the trailer wheels on dollies, as someone suggested, to see if they can get movement with lateral force?
2. Or, Stressor, have you tried the come-a-long test pulling it from different angles than the one you show?
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tluxon
Kirkland, WA
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willald wrote:2. Burbman, myself vs. Ron Gratz and Tluxon, in the argument of whether or not the hensley forms somewhat of a 'virtual' lock from the trailer end, when being pulled on/tensioned. No, its not a complete 100% lock, but due to the forces involved, its pretty close to such. Did you have a swingset when you were a kid? Remember the contraption that 2 people could sit in facing each other and swing to and fro? I believe they still make patio swings that pivot in a similar manner. The seat stays relatively level while allowing a fairly good motion horizontally. If someone really heavy sits in that kind of swing, it takes more to get them swinging, but they can still swing. Now if you take that really heavy kid and have him plant his feet firmly against the ground, it's much more difficult to get him swinging. This is how I see the orange head (or rear bar) of the Hensley, only it has the added benefit of forcing the trailer to pivot opposite the direction it is trying to pivot when applying a lateral force at the hitch.
TeryT wrote:1. Has anyone tried putting the trailer wheels on dollies, as someone suggested, to see if they can get movement with lateral force? Though it sounds good in theory, something tells me this would not work, as the trailer will have a tremendous amount of inertia that you're going to try to spin one way while the linkage only allows lateral movement if it is spinning the opposite way. You'd have to somehow manipulate it such that the head trans-rotates as shown in Dave's video (http://home.comcast.net/~tbluxon/Hensley_Motion_sm.WMV), which I think would be nearly impossible to do with any full size trailer.
Tim
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TnAnFLA
Nokomis FL
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Quote:The net lateral force between coupler and ball is zero. However, since both struts exert a rearward force on the A-frame, the coupler must exert a rearward force on the ball.
Well Ron, we agree half way on this one. There is clearly no net lateral force applied to the coupler by the struts. However I don't think a rearward force is applied either. You are correct when you state that the struts push aft on the a-frame, but at the same time they are applying an equal forward push on the hitch head. Since the coupler is located on the upper element of the hitch head, mounted between the strut attachment points, the two opposing forces cancel out so there is no net force on the coupler in the longitudinal axis. This allows the coupler to provide two functions only. It acts as a "ball joint" in the vertical plane so the A-frame can pivot up and down on uneven road surfaces (e.g., when coming to the bottom of a sloped driveway) and it provides a point to transfer force from the TV along the longitudinal axis during acceleration and deceleration.
The reason I tend to harp on the struts so much is that Hensley states in the installation manual (and I'm paraphrasing) that if the struts are set up incorrectly, you have reduced or no sway control. I think they are an integral part of how this whole system works. And I also think the preload they apply to the hitch head/four bar linkage is an important part of that. I just haven't quite figured out how to put it into a good analytical discussion yet.
Andy
31' Itasca Impulse
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willald
NC
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tluxon wrote:Did you have a swingset when you were a kid? Remember the contraption that 2 people could sit in facing each other and swing to and fro? I believe they still make patio swings that pivot in a similar manner. The seat stays relatively level while allowing a fairly good motion horizontally. If someone really heavy sits in that kind of swing, it takes more to get them swinging, but they can still swing. Now if you take that really heavy kid and have him plant his feet firmly against the ground, it's much more difficult to get him swinging. This is how I see the orange head (or rear bar) of the Hensley, only it has the added benefit of forcing the trailer to pivot opposite the direction it is trying to pivot when applying a lateral force at the hitch.
Yep, had one of those as a kid, and also just built (actually, put together) a swingset for my son, that has one of those. Can't remember what they call it, though.
Excellent analogy, Tim! And I think it proves the point we've been trying to illustrate. The horizontal swing is really the same principle we're talking about here. In both cases, its more than just a simple pendulum motion we're talking about. As it (trailer or horizontal swing) swings to either side, linkage forces the weight (heavy kid, or trailer) to move closer toward the virtual pivot point, making swinging/pivoting considerably more difficult, than it would be with a conventional Pendulum arrangement.
Consider the heavy kid on a conventionl swing also, where he would pivot like a normal pendulum. This would be analagous (spelling?) to what you might have, with a conventional hitch. Much easier for him to get swinging in that case. Why? He's not fighting gravity as directly as he would on the horizontal swing we're talking about, where he has to overcome his own weight/gravity significantly more, in order to swing.
I never suggested that the Hensley is 'locked up' and cannot pivot at all. My point all along was, the force pulling back on the Hensley when towing, makes it very difficult for a trailer to get enough force to pivot much at all, since it has to overcome so much of the pulling force in order to do so. This creates somewhat of a 'virtual' lock, which results in much more pivoting resistance (from the trailer's perspective), than you'd see with a traditional pendulum arrangement (like a Pullrite could be compared to).
Combine that with the benefit of forcing the trailer to pivot the opposite direction it is trying to, and well, there you have it - an ingenius hitch, that will almost never let the trailer induce any pivoting. This I think, explains why this hitch makes towing so much easier.
Can we all agree with this, now? Ron? Don? Tim? Milt? ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/biggrin.gif "biggrin")
Will
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BurbMan
Indianapolis, IN
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Uncle
Uncle
Uncle
I agree, Will!
JK, I really do agree. Good analogy Tim!
Milt, to clarify, here's a photo of the swing Tim was describing:
![[image]](http://home.ripway.com/2005-1/238631/Folder%20Name/Hensleytext006.JPG)
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tluxon
Kirkland, WA
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I'm on board with you, Will, with the sole exception that I believe the Hensley will give you virtually just as much protection from sway when the TT is trying to outrun the TV (pushing rather than being pulled).
As for the side discussion of the struts, the Hensley Installation Manual says,
Quote:HENSLEY ARROW STRUT ADJUSTMENT
IMPORTANT FOR PROPER HITCH PERFORMANCE
The major function of the struts is to hold the Upper Unit (the orange section with the ball mount on it) “square” in relationship to the trailer. When both struts are tight, they will not allow either the Upper Unit or the trailer to pivot from side to side on the ball. It does NOT say that no lateral movement will be allowed. It says there will be no PIVOT (i.e. horizonal rotation or angular change looking straight down on it) allowed. That's how we get a solid tee on the back bar of the linkage. I hope this helps address Milt's concerns.
It goes on to say,
Quote:The struts are correctly adjusted when the Upper Unit is held firmly in a position perpendicular to the centerline of the trailer as shown. It doesn’t have to be absolutely perfect!
BTW, not that it matters so much functionally, but based on the pictures in the installation manual, the struts sure look to me like they're designed to be in both tension and compression. In order to be compression only they would have to be designed as a bushing or sleeve.
Tim
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Ron Gratz
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TnAnFLA wrote:Well Ron, we agree half way on this one. There is clearly no net lateral force applied to the coupler by the struts. However I don't think a rearward force is applied either. You are correct when you state that the struts push aft on the a-frame, but at the same time they are applying an equal forward push on the hitch head. Since the coupler is located on the upper element of the hitch head, mounted between the strut attachment points, the two opposing forces cancel out so there is no net force on the coupler in the longitudinal axis. This allows the coupler to provide two functions only. It acts as a "ball joint" in the vertical plane so the A-frame can pivot up and down on uneven road surfaces (e.g., when coming to the bottom of a sloped driveway) and it provides a point to transfer force from the TV along the longitudinal axis during acceleration and deceleration.
Andy,
Consider the situation where the HA is attached to the TT, but is not attached to the TV. Also assume the WD bars are not attached to the hitch head. If the struts are pushing forward on the hitch head, there also must be an equal force pushing rearward on the hitch head to achieve equilibrium. This rearward force can come only from the A-frame via the ball coupler and ball.
Now assume the TT tires are not chocked and do not offer any rearward rolling resistance. If the struts are pushing rearward on the A-frame, then there must be an equal force pushing forward on the A-frame to achieve equilibrium. This forward force can come only from the hitch head via the ball and ball coupler.
In order to have the struts in compression, in the absence of any external forces on the hitch head or A-frame, you must have the coupler pushing rearward on the ball and the ball pushing forward on the coupler. This will cause the A-frame channels to be in tension.
During towing, the wind and tire drag forces will cause tension in the A-frame channels rearward of the strut attachments. Some of this drag force will be reacted by a decrease of compression in the struts and some of it will be reacted by an increase of tension in the A-frame channels between the strut attachment points and the ball coupler. The amount of drag reacted by struts versus A-frame channels will depend on their relative axial stiffness. The increased tension in the A-frame will increase the rearward force on the ball.
Quote:The reason I tend to harp on the struts so much is that Hensley states in the installation manual (and I'm paraphrasing) that if the struts are set up incorrectly, you have reduced or no sway control. I think they are an integral part of how this whole system works.
I believe it is critical to have the struts adjusted so that the longitudinal axis of the TT is in line with the longitudinal axis of the TV when towing straight ahead. This means the HA's rear unit must be perpendicular to the TT's axis.
If the rear unit is not perpendicular to the TT's axis, the TT will still track nearly straight ahead; but the rear unit will be rotated and shifted to one side. If the rear unit is rotated by, say 3 degrees, the "straight ahead" virtual pivot point will only be moved forward about 24" instead of around 47". This means the "steering moment" will not be reduced as much as is should be. Perhaps even more critical is the fact that the VPP would be shifted to the side of the TV's centerline. This means that any forward thrust from the TT also would be able to exert a steering effect on the TV.
Quote: And I also think the preload they apply to the hitch head/four bar linkage is an important part of that.
Well, I can agree that compression in the struts will preload the ball and coupler. But, I do not see any way for the strut compression to preload the linkage. Again, consider the HA hanging on the end of the A-frame. If there is nothing to push rearward on the linkage, then there cannot be any forward force either. Perhaps we do need more discussion.
Ron
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