Ron Gratz
full time RVer
Senior Member
Joined: 12/27/2003
View Profile
|
BurbMan wrote:*YAWN*
Don, have a couple more cups of coffee and stay with us.
Ron
|
jdwhittaker
York, SC
New Member
Joined: 06/01/2005
View Profile
|
Tim,
Thanks for posting/compressing my video file.
bettered wrote:... Of course we know this is not possible when attached to the TT....
Ed, I think you might mean to say "Of course we know this is not possible under normal circumstances, when attached to the TT.
I say that because this condition can also happen in the event of a slide in which the TT wheels break loose in a turn when the TV wheels haven't.
Perhaps overdriving a turn, or icey slick road conditions could could cause this type of movement, but under normal conditions It can't happen.
Please note that with the HA for a left turn the front end of the TT moves to the left of the centerline created between the TV/TT combo.(opposite to that motion that is a result of sway) while driving straight, as my video and Tim's fig. 3 represent. Also note that with a conventional hitch for the same left turn the front end of the TT moves to the right of the same centerline created between the TV/TT combo(the same direction as the forces caused in sway).
The linkage in the HA is what causes turns to move in this way, and at the same time prevents sway.
Dave
|
Ron Gratz
full time RVer
Senior Member
Joined: 12/27/2003
View Profile
|
jdwhittaker wrote:I am still looking for an explanation of the Virtual Pivot Point, and it's role in all of this, that I can follow. Anybody?
Dave
Dave,
The side links of the HA are attached via pinned (roller bearing) connections at each end. This means that a link can only transmit a pure force (either tension or compression) from the HA's rear unit to its front unit.
The rear unit has no way of knowing how long the link is. The rear unit only is able to respond to the angle at which the force in the link is acting; and that angle is directly in line with the centers of the roller bearings at each end of the link.
This means that, for any given angle of articulation between TT and TV, you could throw away the front unit of the HA and extend the side links until they converge. You then could connect the two links together and to the TV using a pinned connection. The two side links and the rear unit would form a rigid triangle. You would have created an "A-frame" extension of the TT's tongue. The TT now would pivot about the point at which the side links converge and are pinned to the TV.
This, in essence, is what the PullRite does; except that, instead of having an "A-frame", the PR has a solid drawbar connecting the TT to the pivot point. The difference is that the location of the HA's VPP changes as the angle between TT and TV changes.
Ron
|
tluxon
Kirkland, WA
Senior Member
Joined: 08/12/2001
View Profile
 Offline
|
Will, since you started the thread perhaps you could tell us if your questions have been answered or if you'd like anything addressed in more detail. Where would you like to see the thread go from here?
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
|
willald
NC
Senior Member
Joined: 07/15/2002
View Profile
Good Sam RV Club Member
Offline
|
tluxon wrote:Will, since you started the thread perhaps you could tell us if your questions have been answered or if you'd like anything addressed in more detail. Where would you like to see the thread go from here?
Tim
Hehehehe, good question, Tim. ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/smile.gif "smile")
I never imagined this discussion would get so involved, and so detailed. I'm really glad it did, and have really enjoyed reading it (and contributing, where I can). We have some really great, very smart people on this forum. I think we can also chalk this thread up as a good example of how useful these forums can be, and how great information can be shared, if we can stay focused and avoid 'bickering', like what happens in other threads.
I guess my questions originally have been answered, yes. Really, I just wanted specific, geometric/mathematical proof, of the way a Hensley pivots, and where the trailer's pivot point is projected to. I could not ask for that to be covered in any more detail than it has already!
That, and I wondered if there was more to the reasons why the Hensley works so good, besides just the way it projects the pivot point. I think that has been answered too, and the answer is NO - there is nothing else to it. The way the Hensley projects the pivot point, is what gives it the effect of eliminating sway.
As to where the thread should go from here: I don't know. I think there is still some interesting stuff Ron has been discussing, and I'd like to see that continue. Still, if it doesn't (and dies out after this post), I have no complaints. I'm very happy with what we have learned so far with this thread.
I know I originally said this might be a good thread to 'sticky' at the top. Do y'all still think its a good candidate to be stuck at the top? I dunno, we have got into some pretty detailed, technical stuff, that many people may well get bored by (like 'Burbman'..we seemed to put him to sleep...LOL).
Will
|
|
|
Stressor
Whitefish Bay, Wisconsin
Senior Member
Joined: 05/29/2001
View Profile
Offline
|
[quote=Ron Gratz][quote=jdwhittaker]I am still looking for an explanation of the Virtual Pivot Point, and it's role in all of this, that I can follow. Anybody?
Dave[/quote]
Dave,
The side links of the HA are attached via pinned (roller bearing) connections at each end. This means that a link can only transmit a pure force (either tension or compression) from the HA's rear unit to its front unit.
The rear unit has no way of knowing [b]how long[/b] the link is. The rear unit only is able to respond to [b]the angle[/b] at which the force in the link is acting; and that angle is directly in line with the centers of the roller bearings at each end of the link.
This means that, for any given angle of articulation between TT and TV, you could throw away the front unit of the HA and extend the side links until they converge. You then could connect the two links together and to the TV using a pinned connection. The two side links and the rear unit would form a rigid triangle. You would have created an "A-frame" extension of the TT's tongue. The TT now would pivot about the point at which the side links converge and are pinned to the TV.
This, in essence, is what the PullRite does; except that, instead of having an "A-frame", the PR has a solid drawbar connecting the TT to the pivot point. The difference is that the location of the HA's VPP changes as the angle between TT and TV changes.
Ron[/quote]
Can you tell me how this explanation differs in any way from this one?
[quote=Stressor][img]http://home.ripway.com/2005-1/238631/Folder%20Name/Hensley.JPG[/img]
[img]http://home.ripway.com/2005-1/238631/Folder%20Name/Hensley2.JPG[/img]
[img]http://home.ripway.com/2005-1/238631/Folder%20Name/Hensley3.JPG[/img]
Just curious. :B
Note: Due to invalid formatting, all formatting has been ignored.
Milton Findley (and Kerene)
A small piece of my mind...
|
bettered
UpCountry SC
Senior Member
Joined: 07/26/2004
View Profile
|
jdwhittaker wrote:Tim,
Thanks for posting/compressing my video file.
bettered wrote:... Of course we know this is not possible when attached to the TT....
Ed, I think you might mean to say "Of course we know this is not possible under normal circumstances, when attached to the TT.
I say that because this condition can also happen in the event of a slide in which the TT wheels break loose in a turn when the TV wheels haven't.
Perhaps overdriving a turn, or icey slick road conditions could could cause this type of movement, but under normal conditions It can't happen.
Dave
Actually Dave, I meant it exactly the way I said it. This is not even possible under the most extreme circumstances. What the video shows is extreme pivoting to the limit of hitch travel in either direction. Practically, it would be quite impossible to get your trailer out at nearly 90 degrees to your TV and then switch all the way over to the opposite side. I don't care whether it's a Hensley or not, by the time the TT is beside the TV you're both in the ditch on the roof.
Ed
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
|
tluxon
Kirkland, WA
Senior Member
Joined: 08/12/2001
View Profile
Offline
|
A couple years ago in a thread titled "Hensley patent(s), a poster aluded to the possibilty that "no-sway" was originally "less susceptible to sway".
jason_rving wrote:...BTW, look at how he describes his hitch before marketing took hold. Note the absense of the phrase "no-sway" but rather the use of "less susceptible" to sway and "enables the towed vehicle to be moved without significant swaying or fishtailing" ....
"A hitch assembly for coupling a trailer to a tow vehicle includes a mounting member positioned firmly at the rear of the tow vehicle, another mounting member connected to the tongue of the trailer such that it will not turn relative to the trailer about a vertical axis, and a pair of short connecting links which extend between the two mounting members and are pivotally connected to each. The connecting links are of equal length and converge forwardly. This has the effect of placing the effective pivot point for the trailer ahead of the actual hitch assembly, which in turn enhances the stability of the combination tow vehicle and trailer, rendering it less susceptible to swaying or fishtailing in the presence of side winds. "
I'm very curious about this - and maybe it depends on how you define "sway" - but have any of you Hensley owners ever experienced swaying AT ALL in the presence of side winds? I've always had the impression that Hensley owners thought they NEVER had ANY sway, but based on the above text, understanding the behavior of the linkage, and having seen fifth wheels sway in certain kinds of wind, I have a hard time believing that a TT hooked up with a HA isn't capable of a little tail wag now and then as well. Of course with the TV having such a short lever arm, a HA has almost no potential to add anything to a swing of the TT, and actually fights back with the reverse rotation of the resulting translation.
Any confessions out there?
Tim
|
tluxon
Kirkland, WA
Senior Member
Joined: 08/12/2001
View Profile
Offline
|
bettered wrote:jdwhittaker wrote:Ed, I think you might mean to say "Of course we know this is not possible under normal circumstances, when attached to the TT.
I say that because this condition can also happen in the event of a slide in which the TT wheels break loose in a turn when the TV wheels haven't.
Perhaps overdriving a turn, or icey slick road conditions could could cause this type of movement, but under normal conditions It can't happen.
Dave
Actually Dave, I meant it exactly the way I said it. This is not even possible under the most extreme circumstances. What the video shows is extreme pivoting to the limit of hitch travel in either direction. Practically, it would be quite impossible to get your trailer out at nearly 90 degrees to your TV and then switch all the way over to the opposite side. I don't care whether it's a Hensley or not, by the time the TT is beside the TV you're both in the ditch on the roof. So you're saying you couldn't achieve a near-jackknife left to near-jackknife right maneuver in a large empty parking lot? I bet if you gave me a shot I could do it. ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/grin.gif "grin")
Tim
|
bettered
UpCountry SC
Senior Member
Joined: 07/26/2004
View Profile
|
OK, you're on. I'll even come and watch. Your rig, not mine.
Of course we would then have to admit this would be an experiement and in no way anything at all like real life... An "extreme" situation..
Ed
|
|
|
|
