Ron Gratz
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Will,
We agreed to move our HA-related discussions back to this thread; so, here goes.
willald wrote:--- But, the location of the pivot point DOES influence how much steering influence the trailer can have on the tow vehicle, once the trailer does swing out (due to wind or whatever).
We are in complete agreement on that point. If the TT does swing out more than about 10-15 degrees, the HA's pivot point (point of application of lateral force) will have moved back to a location close to the ball coupler. The HA's coupler is about 12" farther from the TV's rear axle due to the extra length of the hitch assembly. Therefore, the lateral force imposed by the TT would be acting on a longer lever arm for the HA-coupled TT than would be the case for a conventionally coupled TT. Therefore, the HA-coupled TT would exert greater steering influence on the TV.
Please keep in mind that the HA's pivot point location advantage quickly goes away when the angle between TV and TT is greater than a few degrees. This is unlike a PullRite which has a fixed pivot point location for all TV/TT yaw angles.
Ron
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willald
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Ron Gratz wrote:If the "can't swing because it can't move toward the pivot point" theory is correct, then no pendulum can swing because gravity would not allow the mass to move upward. Galileo Galilei could not have invented the pendulum and we would have had no pendulum clocks.
#$%*#$@!, somehow I knew you were going to confuse things, throwing up the pendulum arrangement. I shoulda addressed that as part of what I said.
Look closely again at the video, that shows the range of motion the Hensley goes through. Then, look at it again. Then, look at it one more time, Ron. Then one more time. ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/smile.gif "smile")
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. 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. 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.
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.
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
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willald
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Ron Gratz wrote:If the TT does swing out more than about 10-15 degrees, the HA's pivot point (point of application of lateral force) will have moved back to a location close to the ball coupler. The HA's coupler is about 12" farther from the TV's rear axle due to the extra length of the hitch assembly. Therefore, the lateral force imposed by the TT would be acting on a longer lever arm for the HA-coupled TT than would be the case for a conventionally coupled TT. Therefore, the HA-coupled TT would exert greater steering influence on the TV.
We are in agreement there, too. If the trailer gets to these extreme angles, the Hensley would indeed allow an even longer lever arm, allowing for even greater steering influence on the TV.
However, thats like the old saying about, "If a bull frog had wings...." It will NEVER happen, unless something so major and disastrous hits, no hitch of any kind woud save you, regardless. Like maybe, the back of your trailer getting hit with a 200 mph Hurricen-style wind, to negate the 'pulling' effect between truck/trailer? Yeah, that could potentially put the Hensley in this situation, but if you're travelling in that kind of wind, you're pretty much screwed, no matter what you're driving.
As Don and I are trying to illustrate, the Hensley's design insures that this (extreme yaw angle) will NEVER happen as long as the tow vehicle is 'pulling' on the trailer, except when the tow vehicle initiates the turning (meaning, in a tight turn where it is going slow).
Quote:Please keep in mind that the HA's pivot point location advantage quickly goes away when the angle between TV and TT is greater than a few degrees. This is unlike a PullRite which has a fixed pivot point location for all TV/TT yaw angles.
And, as I said, the point where that advantage goes away, will almost NEVER happen, due to the Hensley's design, and the path through which it pivots. It could happen if there was no tension between the tow vehicle and trailer, and I think thats the point we really need to keep in mind here, thats been overlooked before.
Yes, the PullRite has a fixed point location, and behaves just like a 5er. This gives great stability, too, and perhaps a bit less complex. However, it does NOT give the same effect of 'locking' the trailer in a straight line, like the Hensley does.
Will
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Ron Gratz
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In the Accident on I95 thread, it was suggested that a HA would have forced the trailer to pivot similar to a 5th wheel and that using a HA would have prevented the wind from swinging the trailer. I responded with:
Will,
The HA does not force the trailer to pivot similar to a 5th wheel in the first 15 degrees. When the TV and TT are aligned straight ahead, the HA moves the pivot point ahead about 47" and not all the way to the TV's rear axle as a 5th wheel does. Also, at an angle of about 4 degrees, the pivot point is only moved forward about 24". Beyond 4 degrees, the pivot point quickly moves back close to the location of the ball coupler.
The location of the pivot point is of little or no consequence in determining whether the wind can cause the trailer to swing. An important factor is the distance between the TT axles and the center of pressure of the wind force. For a typical TT, having the pivot point farther forward means that the axles and wind force would be relatively closer together. This would make it somewhat easier for the wind to swing the TT. This means that, if anything, the HA would give a slight disadvantage relative to a conventional hitch.
Ron
Will responded with:
I do NOT for the life of me follow you on that one, but even if such is true, the HUGE advantage the Hensley gives in that the trailer is forced to pivot such that it cannot influence the tow vehicle as much, FAR outweighs any slight disadvantage that (may or may not exist) regarding wind. And, I have way too much experience towing with the Hensley in windy situations, to believe your suggestion here, anyway. I think you dreamed that one up.
No, Will, I did not dream that one up.
Consider a TT having a body length of 30 ft. Assume the axles are located according to a 60/40 rule putting the axles center at 18 ft behind the front of the body. Assume the center of a wind force of 1000# acts at the midpoint of the body, 15 ft behind the front. Assume the ball coupler is 4 ft ahead of the front of the body.
For a TT which pivots at the ball coupler, the tires would have to exert a force of 1000x(15+4)/(18+4) = 864# to achieve equilibrium.
If the TT had a Hensley hitch, the "straight ahead" pivot point location would be about 8 ft ahead of the front of the body. In this case, the tires would have to exert a force of 1000x(15+8)/(18+8) = 885#.
Therefore, the added effective tongue length, resulting from the use of the HA would be a slight disadvantage as regards the ability of a cross wind to swing the TT.
Please keep in mind that my example deals with how the HA affects the TT's ability to be swung by the wind and not how the HA affects the lateral forces imposed by the TT on the TV. As I explained in a previous post, if the TT swings more than 10-15 degrees, the HA also is at a disadvantage regarding the TT's steering effect on the TV.
Ron
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willald
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Ron Gratz wrote:As I explained in a previous post, if the TT swings more than 10-15 degrees, the HA also is at a disadvantage regarding the TT's steering effect on the TV.
And as I explained, that 'if the TT swings more than 10-15 degrees with the Hensley', is like the 'If a bull frog had wings...' analogy. LOL!
The Hensley design prevents this from EVER happening, unless the tow vehicle initiates the turning (or something takes away the 'tension' between truck and tow vehicle).
Will
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Ron Gratz
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willald wrote:And, as I said, the point where that advantage goes away, will almost NEVER happen, due to the Hensley's design, and the path through which it pivots. It could happen if there was no tension between the tow vehicle and trailer, and I think thats the point we really need to keep in mind here, thats been overlooked before.
Yes, the PullRite has a fixed point location, and behaves just like a 5er. This gives great stability, too, and perhaps a bit less complex. However, it does NOT give the same effect of 'locking' the trailer in a straight line, like the Hensley does.
Will
Well, Will, let me try another approach.
When the HA-equipped TT and TV are aligned straight ahead, the HA's two side links, if extended forward, would converge at a point located on the TV's centerline and about 47" ahead of the ball coupler. So, lets just replace the two 5"-long side links and the HA's lower (front) unit with two 47"-long side links which converge at the same angle and are attached to each other at their front ends and to the TV via a pinned connection.
In essence, we have just converted the HA to a PullRite. Instead of having a 4-bar linkage, we now have the TT attached to the TV via a rigid triangle (an "A-frame") attached to a pivot point 47" ahead of the ball. For the "aligned straight ahead" condition, the HA's 4-bar linkage functions as though it were a 47"-long extension of the TT's tongue with a pivot point at the front end. Kinematically, it functions the same as a PR hitch and, as you have agreed, the PR does not have any "locking" effect. Neither does the HA.
The "pulling tension" on a conventionally coupled TT does not "lock" it from swinging; the "pulling tension" on a PR-coupled TT does not "lock" it from swinging; and the "pulling tension on a HA-coupled TT does not "lock" it from swinging. On all TTs, it is only the lateral force on the tires and the TT's inertia which control the swinging.
Ron
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Ron Gratz
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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.
Quote: 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".
Quote: 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.
Quote: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:
Quote: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
* This post was
edited 08/23/05 05:38am by Ron Gratz *
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Stressor
Whitefish Bay, Wisconsin
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Why argue with someone who does not own a Hensley, has never towed anything with a Hensley, has never taken one apart, never experimented with one, and who answers everyone who has with spurious argument?
"Is there something about the "tension/pulling between tow vehicle and trailer" which I have missed?"
Why yes Ron, when it was presented to you, with pictures, you posted about one and a half printed pages to the effect that it couldn't happen. And, yet, it did. Don't let empirical proofs get in the way of your expounding on your ill-informed theory though.
Milton Findley (and Kerene)
A small piece of my mind...
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BurbMan
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OK Ron, let's talk about the pendulum. In theory, both an HA-equipped TT and a pendulum pivot similarly. However, you start a pendulum by raising it in its arc, and releasing it to let gravity start the motion. With the HA, the trailer itself creates resistance to motion.
Picture a pendulum with a rubber band connected to its bottom and the other end fastened to the ground surface below the pendulum. Any attempt to start the pendulum swaying along its arc will be resisted and eventually stopped by the force the rubber band exerts. The rubber band will effectively dampen the movement until the pendulum is once again hanging in a static position.
What Will and I are saying is that the drag and wind resistance created by the trailer act just like the rubber band in my example. Traveling at hiway speed, these forces amount to the equivalent of a very thick rubber band on the bottom of that pendulum, so any attempt to swing the pendulum is quickly dampened by the rubber band.
Ron, I don't disagree with the math that you introduce to this discussion, but I think that your calcs become largely theoretical with regard to this topic (bullfrog with wings?)...
Yes, the math says that movement is allowed, but you are ignoring the fact that the HA relies on tension bewteen the TV and TT to resist any movement introduced into the 4-bar linkage by the TT.
AND, it's not a question of whether the TT is allowed to pivot...as an example, if I am driving on the interstate at 70 mph with the HA connected to my 34' TT, and a 50 mph gust of wind comes up perpendicular to the trailer, I will feel the TT move. HOWEVER, the HA effectively dampens this movement to a single push, and this tension that Will and I are trying to explain prevents that intial movement from repeating itself into a sway condition, as a pendulum would when dropped from a point along its arc.
Ron, it's clear that you understand the physics of the HA, but as Milt said, I think your lack of direct experience as an HA user is hindering your ability to see the applied result of these principles.
Don
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willald
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BurbMan wrote:What Will and I are saying is that the drag and wind resistance created by the trailer act just like the rubber band in my example. Traveling at hiway speed, these forces amount to the equivalent of a very thick rubber band on the bottom of that pendulum, so any attempt to swing the pendulum is quickly dampened by the rubber band.
Actually, its a bit more than just the pendulum analogy with a rubber band pulling at the bottom. To accurately account for the way the Hensley is pivoting, you'd have to also say that the arm of the pendulum has mechanical linkages in it, that make it extend/contract to become shorter whenever the pendulum swings out, and at its max length when straight. This is why there is so much more force required to make a trailer induce any pivoting with a Hensley, than with a conventional hitch. The trailer literally has to move FORWARD (more so than the pendulum analogy suggests), against all wind resistance and friction, in order to pivot.
As Ron pointed out, really, any hitch will give you the same 'pendulum' effect, of resisting pivoting. The Hensley goes beyond that, though, in that as the pendulum 'swings', the arm is essentially shortened, making it much, much more difficult for the trailer to induce any pivoting.
Quote:Ron, I don't disagree with the math that you introduce to this discussion, but I think that your calcs become largely theoretical with regard to this topic (bullfrog with wings?)...
Yes, the math says that movement is allowed, but you are ignoring the fact that the HA relies on tension bewteen the TV and TT to resist any movement introduced into the 4-bar linkage by the TT.
I agree. It kind of reminds me of the story about the bumble bee. On paper, and according to scientists who analyze such, it shouldn't fly at all. Better not tell the bumblebee that, though. ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/biggrin.gif "biggrin")
Will
P.S.: Milton/Stressor, I understand your frustration, but please try to go easy on Ron. This has been a very civil, intelligent, respectful discussion so far, lets keep it that way. Everyone's input is valued and respected (even though ours is the only one that is right..Hahahahaha, J/K!!)
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