BurbMan
Indianapolis, IN
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Hey, what happened to putting dollies under the wheels on Will's TT and watching him do figure 8's in the Winn Dixie parking lot while I drink a beer and man the video camera ???
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willald
NC
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BurbMan wrote:Hey, what happened to putting dollies under the wheels on Will's TT and watching him do figure 8's in the Winn Dixie parking lot while I drink a beer and man the video camera ???
LOL! We can do that, too, Don, I'll never turn down an opportunity to drink beer with a fellow camper! ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/smile.gif "smile")
However, I think we concluded earlier, that this test really prove what we wanted it to, and wouldn't accomplish much (except for consuming some beer, and making the neighbors around think we were a bunch of nutcases...LOL!)
Will
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TeryT
Scottsdale AZ
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willald wrote:BurbMan wrote:Hey, what happened to putting dollies under the wheels on Will's TT and watching him do figure 8's in the Winn Dixie parking lot while I drink a beer and man the video camera ???
LOL! We can do that, too, Don, I'll never turn down an opportunity to drink beer with a fellow camper!
However, I think we concluded earlier, that this test really prove what we wanted it to, and wouldn't accomplish much (except for consuming some beer, and making the neighbors around think we were a bunch of nutcases...LOL!)
Will Let's do it! Aarrhhhh - beeerrr!
Mighty 4Runner Sport V8 4x4 - over 200k
Hensley Hitch
McKesh Mirrors, Geolandar G015 Tires
Hopkins Insight Brake Controller
Tranny: Hayden Cooler/Fan & CyberDyne Gauge
Mobil 1 Full Synthetic fluids everywhere!
Rockwood 2502 Ultralight TT (3600 lb. dry)!
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BurbMan
Indianapolis, IN
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Ok, Captain Bringdown! I guess I'll drink a beer and man the video camera while you hang the HA vertiaclly and attach an anvil to it. Sounds like the script for an Itchy and Scratchy cartoon! LOL!
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tluxon
Kirkland, WA
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I decided to put a little work into seeing what arc the coupler travels through as the trailer rotates in a "swing". It took a little time to construct the points so I stopped at 8 degrees in each direction.
![[image]](http://www.luxony.com/webpics/Hensley_Fig6.jpg)
What I learned from this is that in the first 8 degrees of swing, the coupler gets 2.15 inches closer to the tow vehicle. This simulates a pretty short pendulum which makes the lifting wedge angle fairly steep. It appears to me that a strong tension between the TV and TT would work quite effectively at keeping the angle within a few degrees of center. I'm curious to hear what Ron has to say about it.
Tim
Tim -
wife Beverly & 2 boys who love camping
2002 K2500 Suburban 8.1L 4.10 Prodigy
2005 Sunnybrook 30FKS HP Dual Cam
Replaced 2000 Sunnybrook 26FK on 8/6/04
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Ron Gratz
full time RVer
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willald wrote:Once we have all this in place (hahahaha!), all we'd have to do is try to push the A frame/weight side to side. You would find, that if it is a real heavy weight, it would be very difficult to pivot the A frame back and forth, because you'd have to overcome all the weight/gravity pulling down, since the Hensley's pivoting arc/path would make you in essence lift up the weight in order to pivot it either direction.
This is the point Ron refuses to believe - he thinks the pulling force on the Hensley makes no difference, and the force required to swing such, would be no different than what you'd experience on a conventional pendulum arrangement. It is NOT the same as a conventional pendulum arrangement, because the Hensley forces the trailer to be pulled closer to it, in order for it to swing either way. It would be like a pendulum arrangement, where the pendulum arm has linkage/mechanism in it, that makes the arm 'reel in'/get shorter, when swinging to either side.
Will,
You are mostly correct in principle; but you are greatly overestimating the magnitude of the weight/pull effect.
The "reel in" effect amounts to about 0.1" of forward movement of the ball for 1 degree of swing angle. This does not result in any appreciable resistance to swinging. The larger amounts of forward movement of the ball seen in the video are for swing angles which are much larger than those encountered at highway towing speeds; but even those larger forward movements, if they could be achieved at highway speeds, would not result in any appreciable resistance to swinging.
As far as regular pendulum versus 4-bar pendulum -- with either an ordinary pendulum or one supported by a 4-bar linkage, a very close approximation of the force required to swing the weight is given by:
Force = weight X tangent of angle of swing
For an angle of 1 degree, the tangent is about 0.017. So, if your test anvil weighs 100#, you will need to apply about 1.7# of force for each 1 degree of swing.
Please re-read this post if you want more details.
If you want to conduct a meaningful test, just reproduce Milt's test. But pull on the ball where the real force is applied; and pull at a few different angles which are not lined up to pass through the VPP.
Ron
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Ron Gratz
full time RVer
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tluxon wrote:I decided to put a little work into seeing what arc the coupler travels through as the trailer rotates in a "swing". It took a little time to construct the points so I stopped at 8 degrees in each direction.
What I learned from this is that in the first 8 degrees of swing, the coupler gets 2.15 inches closer to the tow vehicle. This simulates a pretty short pendulum which makes the lifting wedge angle fairly steep. It appears to me that a strong tension between the TV and TT would work quite effectively at keeping the angle within a few degrees of center. I'm curious to hear what Ron has to say about it.
Tim
Tim,
I agree with your numbers. I might also mention that, for the 8-degree swing, the VPP will be about 13" left and about 13" forward of the centered ball location.
Please keep in mind that this phase of the thread began with a discussion of how much wind force would be required on the side of a HA-equipped TT to make it swing against the "resistance of the hitch".
Lets assume that a "drag" force of 1000# acts through the ball at the 8 degree angle. This rearward force will act on a moment arm of about 1' relative to the location of the instantaneous center of rotation (a.k.a. VPP). It will produce a CW moment of about 1000 ft-lb.
Lets assume the TT body length is about 30' and the center of the right-directed wind force acts at about 20' rearward of the VPP. The required wind force is 50#.
Therefore, even at this rather large TT yaw angle, a wind gust could easily overcome the HA's "yaw resistance". It's good that the TT's tires are there to provide the swing resistance that the HA cannot.
Now, if you want to evaluate the dynamic force added by the "reel in" effect, you could use the method I presented in the link found in my previous response to Will.
Ron
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tluxon
Kirkland, WA
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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
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Ron Gratz
full time RVer
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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
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Ron Gratz
full time RVer
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drfife wrote:Ron:
Have you studied a Hensley hitch in person? I think you would benefit to see how it is engineered and functions if you did.
Look around the campground for a trailer with a Hensley. I can just about promise you that the owner would let you look at it and play with it to your hearts content.
Russell,
Thanks for the advice. I am always on the lookout for a HA-equipped TT, but they're a little hard to find. In the past five years, I've spotted four of them. In fact, I followed one of them for 20 miles on I-10 (can't remember if it was NM or AZ) until he pulled into a rest area. I talked to the owner about his HA, mentioning that the rear of the TT seemed to be moving side-to-side in the cross wind. He said the movement was not uncommon; but he did not feel it in the the truck.
All four owners seemed to be quite happy with their HAs. One stated he did not feel it was much of an improvement over his Dual-Cam. One expressed displeasure with the difficulty of the hitch-up process (perhaps he needs one of your mirrors).
As far as learning about how the HA works from these four owners, I got nothing more than what I can read in the Hensley marketing materials. Their experiences and impressions were remarkably similar. All said that the HA actually eliminates sway; whereas other hitches only control sway.
When I asked them how the hitch works, I received a variety of answers. One said that the HA contains "cams" which lock when towing straight ahead and unlock for sharp corners and backing. One said the HA makes the rig "act and think like a straight truck". A couple said something to the effect that the hitch could only be controlled by the TV and not by the TT. One said he knew that the HA "used geometry" to eliminate sway, but was not sure how. They all suggested I should request a copy of the Hensley video if I really want to know how the hitch works.
After talking with these owners, I felt that I could get much more information from the Hensley Patent Documents and from photos and videos such as the one posted by Tim showing how freely the rear unit moves relative to the front unit when not attached to a TT.
It might be difficult for non-engineers to understand diagrams and photos; but I feel quite confident that I know how the HA does and does not work based on the patent papers. One exception is that the patent document describes the struts as "turnbuckles" and does not say if they are used in tension or compression. I assumed tension; and the truth is otherwise. Fortunately, as far as operation of the hitch is concerned, it makes no difference as long as both are tight.
I'll keep looking for HAs and, on the rare occasion when I spot one, I'll impose on the owner to tell me how the hitch works. Hopefully, one day I'll find one who knows.
Ron
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