bettered
UpCountry SC
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Stressor wrote:Tim,
If it can be demonstrated empirically, the theory needs to accomodate what is actually happening to be a valid theory. That is what theories do.
You've got the right idea here, but it's the other way around. The scientific approach is to generate a theory to describe a phenomenon and then design experiments and collect relevant empirical data to prove the theory works. The theory need not 'accomodate' whatever empirical data you select, the experiment has to be designed to produce data such that the theory is proven valid or disproven.
Stressor wrote:The point of fixity when towing is point C, representing your tow vehicle with all of its mass and resistance to changing direction. Holding DE and AB to a fixed length makes them rockers in 4-bar parlance, and while C does not exist physically, except as the entire mass of the TV as it is attached at the hitch receiver, the linkage acts as if it is a rigid connection. That the legs are fixed, rigid entities to a pulling force was demonstrated by a come-a-long and a willow tree.
Point C is imaginary. It's a conceptual or virtual point that describes the actions of the linkage. It represents only the theroretical ellipse traced by the locii of intersections of the links, and gives us some understanding of the directions in which the force vectors are acting.
Stressor wrote:In operation, if a force is applied to the travel trailer sufficient to move C, the entire rig moves to the side. This is something no Hensley owner will argue.
Since 'C' is imaginary, the only force that can be applied to it is an imaginary force. Forces act on bodies.
Stressor wrote:That the links pivot as demonstrated if point C is moved, by turning a steering wheel for example, is what you are all calling translation. The links move to the side.
That's certainly not what I'm calling translation. From a straight ahead position of the TV/TT combination, the initial movement of the black part relative to the orange part has can only be in translation, i.e. sideways. As the links move, the rotationsl effects become apparent.
Stressor wrote:At approximately 30 degrees angular difference between the TV and the TT, the links are fully extended, translated if you will, and continued turning beyond that causes the links to rotate until they run into themselves at about 75 degrees TV/TV angular difference in the real world.
There ain't no magic.
The only 'magic' I was referring to (and why I put it in quotes) is that coming from Adam Smith's invisible hand. We buy things of perceived value when the price is acceptable to us. If the price is 'too high' we don't buy. That Hensley stays in business is proof that 'enough' people perceive adequate value in the hitch at its current price.
Ed B
BetterEd
DW + 2 grandkids + Mini Schnauzer
2005 Chev 3500 Crew D/A 6.6L LLY, 6 x 6 DRW, 3.73
Tru-Flow + Banks, 2005 Flagstaff 831FKSS
Hensley + Prodigy
"Genius may have its limitations...." E. Hubbard 1856 - 1915
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Stressor
Whitefish Bay, Wisconsin
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Bettered,
Thank you for clearing all that theoretical stuff up for me. I will not take this to work, because they call me professor there and I teach all sorts of theories to unsuspecting students. I will be happy to discuss the philosophy of knowledge with you, send me a PM. ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/biggrin.gif "biggrin")
There is no appreciable loci of ellipse when pulling, because there is no pivoting, no translation, and the connection is as rigid as a steel bar can make it. There is a loci of ellipse when backing up or turning.
You said, "Since 'C' is imaginary, the only force that can be applied to it is an imaginary force. Forces act on bodies." I say, "The hitch receiver is on the way to point C, lend me a portion of your anatomy to use as a shim in the receiver, and you can talk to me about your imaginary forces while I crank the come-a-long." (I have a portion of your anatomy in mind. ).
Translation only occurs if C moves left or right, and that only happens if C is moved left or right by the steering mechanism of the truck. What I have been trying to get across is that there is no translation when the TV is pulling the TT.
You will destroy the hitch before it will translate a millimeter. The linkage does not bend, shift, wiggle, or anything else from the TT end, it is as if it were constructed of a rigid steel bar. (It is).
The black part, the TV end, moves as points DE move in the diagram above, if and only if the TV is turned. The black part moves not at all if the trailer provides the input. This is called a locked linkage, and believe me, it is locked. (See the picture with the come-a-long). I think we said the same thing, and it appears that you did say that the translation is a sideward movement.
![[image]](http://home.ripway.com/2005-1/238631/Folder%20Name/Hensleytext006.JPG)
Please point out any translation you see in the photo above.
I know all about Adam Smith. This ain't like that, this is about how a linkage works. Start a thread about whether or not the Hensley is worth it or read the 55 that already exist.
Milton Findley (and Kerene)
A small piece of my mind...
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tluxon
Kirkland, WA
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Stressor wrote:...you are all calling translation...
Oops, my bad. Technically, translate means to move without rotation, while I was using it as a shortcut word to describe the translation and very slow simultaneous rotation of one end bar with respect to the other. The linkage simply doesn't allow translation or rotation in isolation of each other, so either you get them both or you get neither. Perhaps I should go back and correct all my posts by replacing the word "translate" with "trans-rotate" and footnoting my made-up definition.
Stressor wrote:At approximately 30 degrees angular difference between the TV and the TT, the links are fully extended, translated if you will, and continued turning beyond that causes the links to rotate until they run into themselves at about 75 degrees TV/TV angular difference in the real world. Actually, the sketch I made in SolidWorks shows that the furthest the rear bar translates with respect to the front bar is when the short side link to that side is perfectly aligned with the front bar, which is right at 15 degrees.
![[image]](http://home.comcast.net/~tbluxon/HensleyLink_at_15deg.jpg)
At 29-30 degrees the short link to that same side has continued to rotate to be aligned with the rear bar (the tee of the TT).
![[image]](http://home.comcast.net/~tbluxon/HensleyLink_at_29deg.jpg)
At just over 73 degrees, the geometry of the linkage cannot accommodate any further rotation without elongation of the side bars or shortening of the long tee bar or lengthening of the short tee bar.
![[image]](http://home.comcast.net/~tbluxon/HensleyLink_at_73deg.jpg)
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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Stressor
Whitefish Bay, Wisconsin
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Whatever Tim, the fact is that the links are at 90 degrees to the hitch bar when the angular difference between the Tow vehicle and travel trailer is approximatly 30 degrees.
I have a Hensley Arrow Hitch, and I looked and I measured.
I don't know where Ron gets his stuff, and last time we talked, he was still swearing that the upper orange hitch assembly pivoted on the ball.
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tluxon
Kirkland, WA
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You know, Milt. You ought to mount a video camera on your truck and take the HA and your TT for a spin. Focus the camera on the hitch head and record how it behaves at different times during your trip. I think you'll be surprised to see just how much it "translates" (moves side-to-side) as you accelerate and brake (creating both tension and compression in the linkage) during your maneuvering. Unless the linkage pins are tight as a drum, you should see plenty of slight (and perhaps not-so-slight) side-to-side movement back there. What you won't notice is anything resembling sway, but don't mistake this for no movement at all.
Or is that just another one of my entertaining ideas that there's no point in trying "in the real world"?
Tim
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bettered
UpCountry SC
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Stressor wrote:Bettered, ...I will not take this to work, because they call me professor there and I teach all sorts of theories to unsuspecting students.
This must be where the theory of "dumbed down" is coming from...
Stressor wrote:There is no appreciable loci of ellipse when pulling, because there is no pivoting, no translation, and the connection is as rigid as a steel bar can make it. There is a loci of ellipse when backing up or turning.
And of course you're not pulling when you're turning...
Stressor wrote:You said, "Since 'C' is imaginary, the only force that can be applied to it is an imaginary force. Forces act on bodies." I say, "The hitch receiver is on the way to point C, lend me a portion of your anatomy to use as a shim in the receiver, and you can talk to me about your imaginary forces while I crank the come-a-long." (I have a portion of your anatomy in mind. ).
Very cute.
Stressor wrote:Translation only occurs if C moves left or right, and that only happens if C is moved left or right by the steering mechanism of the truck. What I have been trying to get across is that there is no translation when the TV is pulling the TT.
Lucky students. You're so anxious to talk that you cannot listen. The Orange part of the hitch will initially and ONLY be translated left or right upon initiation of any turn, in any direction, going forward or backward from a straight line between the TV and TT. I think that's exactly what I said earlier, but maybe the way I said it was faulty. P.S. Nobody learns much of anything when they're talking.
Stressor wrote:You will destroy the hitch before it will translate a millimeter. The linkage does not bend, shift, wiggle, or anything else from the TT end, it is as if it were constructed of a rigid steel bar. (It is).
Actually, it isn't.
Stressor wrote:The black part, the TV end, moves as points DE move in the diagram above, if and only if the TV is turned. The black part moves not at all if the trailer provides the input. This much is absolutely correct. But then you go off the reservation, so to speak...
Stressor wrote: This is called a locked linkage, and believe me, it is locked.
We used to have a saying when I was flying (nearly 40 years ago) called head down and locked. I won't bother to explain...
Stressor wrote:(See the picture with the come-a-long). I think we said the same thing, and it appears that you did say that the translation is a sideward movement.
Please point out any translation you see in the photo above.
I know all about Adam Smith. This ain't like that, this is about how a linkage works. Start a thread about whether or not the Hensley is worth it or read the 55 that already exist.
Question is whether or not chasing this particular rabbit down the hole is worth pursuing. It's kind of like trying to teach a pig to dance. Before long, you begin to realize that the pig likes it!..
Anyway, Read some more of Mr. Gertz. I for one am glad he's back. We can all learn from each other, but only when our brains are unlocked.
Sincerely and respectfully,
Ed B
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bettered
UpCountry SC
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Stressor wrote:Whatever Tim, the fact is that the links are at 90 degrees to the hitch bar when the angular difference between the Tow vehicle and travel trailer is approximatly 30 degrees.
I have a Hensley Arrow Hitch, and I looked and I measured.
I don't know where Ron gets his stuff, and last time we talked, he was still swearing that the upper orange hitch assembly pivoted on the ball.
Wow! Tim is right. You and Ron may need to have another look. Those big locking nuts that we tighten up on the drag bars pretty much (absolutely) prevent any (and all) rotation at the hitch ball in the horizontal plane, while permitting rotation in the lateral plane, i.e. when the TV / TT are moving over undulating ground that causes the vertical angle of the TT relative to the TV to change. That's WHY the hitch works, and it's the ONLY reason it works...
Ed B
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Stressor
Whitefish Bay, Wisconsin
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Ed,
Mr. Gratz does not understand the linkage. I have read his remarks for some time, and his understanding of the hitch is imperfect. Some of it he has down very well, but he is unable to visualize the operation in use. He still thinks the hitch pivots on the ball.
Here is a quote from him:
,..." The rear link, which actually is the upper (rear) housing, does move side to side and the ball is securely attached to it. When the rear link moves, the ball also must move. It makes no difference whether the ball moves about 5" to one side or moves precisely 4.768" to one side. The point is – the ball does move side to side. The figure of 4.768" derives from the assumption that the front pins are 7.125" center to center, the rear pins are 7.875" center to center, and it is 5.000" center to center from a front pin to a rear pin. If you prefer to use different numbers and different tolerances, I can provide the corresponding maximum side to side movement.
This statement can only be true if the rear struts are very, very loose.
As for my students, to their credit several of them are in doctor school at this time, so my understanding could not have hurt them appreciably.
I believe that the correct expression is "head up and locked."
Now, Ed, would you kindly add to the discussion rather than poke holes? Do you own a Hensley? How do you think it works?
You have not addressed the lack of translation in the hitch picture. The application of a very large off center rotational force from the travel trailer end of the linkage has not resulted in any rotation, translation, or what have you. What is your explanation for this? You say it is not locked up, can you explain the lack of movement?
* This post was
edited 06/07/05 04:20pm by Stressor *
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bettered
UpCountry SC
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Stressor wrote:Ed,
Mr. Gratz does not understand the linkage. I have read his remarks for some time, and his understanding of the hitch is imperfect. Some of it he has down very well, but he is unable to visualize the operation in use. He still thinks the hitch pivots on the ball.
Here is a quote from him:
,..." The rear link, which actually is the upper (rear) housing, does move side to side and the ball is securely attached to it. When the rear link moves, the ball also must move. It makes no difference whether the ball moves about 5" to one side or moves precisely 4.768" to one side. The point is – the ball does move side to side. The figure of 4.768" derives from the assumption that the front pins are 7.125" center to center, the rear pins are 7.875" center to center, and it is 5.000" center to center from a front pin to a rear pin. If you prefer to use different numbers and different tolerances, I can provide the corresponding maximum side to side movement.
This statement can only be true if the rear struts are very, very loose.
As for my students, to their credit several of them are in doctor school at this time, so my understanding could not have hurt them appreciably.
I believe that the correct expression is "head up and locked."
Now, Ed, would you kindly add to the discussion rather than poke holes? Do you own a Hensley? How do you think it works?
I think you may be misinterpreting Ron's remarks. While the ball does NOT move RELATIVE TO THE Orange part of the hitch, it surely does move (initially in translation) every time you turn - even a little.
Please remember my comment about the bird flying directly over the hitch looking down. He has to fly a serpentine path to stay over the hitch as the TV turns from side to side. From the birdeye view, the ball can and does translate as far as the links will allow it to - some 11 inches by my reckoning.
I suggest you have someone else drive (S L O W L Y) your vehicle in a parking lot, make some small turns while you walk along side. Watch the hitch at work. It's really quite interesting, not to say 'magic'.
As for the airplane analogy, one can either be fixated on the scenery or on the instruments, but neither is healthy for very long. You must do both - continuously and for as long as you are flying. Gear down, gear up. Makes no difference until you need them (or don't). Same goes for the eyes and the human processor.
Yup I have a HA, and I knew pretty much how it worked before I bought it. Actually, I did the above exercise with a friend's rig before I bought the hitch. Of course, I know a lot more about it now..
One thing I do know is that the linkage only locks at about 80 degrees to one side or the other. But that's enough for me...
Ed B
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Stressor
Whitefish Bay, Wisconsin
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tluxon wrote:You know, Milt. You ought to mount a video camera on your truck and take the HA and your TT for a spin. Focus the camera on the hitch head and record how it behaves at different times during your trip. I think you'll be surprised to see just how much it "translates" (moves side-to-side) as you accelerate and brake (creating both tension and compression in the linkage) during your maneuvering. Unless the linkage pins are tight as a drum, you should see plenty of slight (and perhaps not-so-slight) side-to-side movement back there. What you won't notice is anything resembling sway, but don't mistake this for no movement at all.
Or is that just another one of my entertaining ideas that there's no point in trying "in the real world"?
Tim
Tim,
I will simply state that translation will only occur if the tow vehicle changes direction. It will not translate at all if the travel trailer initiates the directional change. In operation the rear of the travel trailer moves very little, until the steering wheel is turned.
A TV camera would be nice, but Hensley did that already and it shows a lot of translation as the tow vehicle travels in and around a series of pylons.
My rear glass, held down with a bungy cord, mirrors my hitch very well, and it does not translate at all during straight ahead pulling.
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