Ron Gratz
full time RVer
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TnAnFLA wrote:Ron, it seems to me that if the struts were missaligned by 5 degrees or so then the TT would track straight, but off center along the arc defined by the 5 degree misalignment. In other words, the head would translate enough right or left to account for the misalighnment in order to balance out the forces on the four bar linkage.
Andy,
I agree almost completely. If the rear unit has moved off center, the asymmetry of the linkage will result in a small restoring force which will tend to reduce the yaw angle. That's why I suggested the TT would track at close to zero but not exactly zero angle. That means the rear unit would remain rotated to nearly 5 degrees.
Ron
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TnAnFLA
Nokomis FL
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Joined: 02/18/2005
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Ron, I think you've got it backwards. When you snug up the struts, you tighten the locknut on the strut and put a force on the outer sleeve of the strut that pushes towards the rear of the A-frame, and the screw that you're turning the lock nut on is pushed forward into the hitch head. So the forward end of the strut is compressing the hitch head and the aft end is compressing the strut mount. As I noted above, you "tension" the unit by expanding the strut. And if my recollection of physics is accurate (not a sure bet at all) the net force on the coupler/ball should be zero if both struts are of equal length. Both struts are "pushing" with equal force on opposite sides of the ball coupler.
Andy
31' Itasca Impulse
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Ron Gratz
full time RVer
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bettered wrote:--- But it's my opinion that there's a significant difference between some lateral force resisting sideways movement of the TT through the tires, and no resistance at all.
Ed,
I agree. And what I'm saying is that, for a rolling tire, unless there is some yaw angle, there is no resistance at all.
If a TT has a CCW yaw, a tire's lateral force acts to the TT's left. If a TT has a CW yaw, the tire's lateral force acts to the TT's right. The magnitude of the lateral force is proportional to yaw angle and must pass through zero when the yaw angle is zero.
Quote:Because the sine and tangent for small angles are nearly identical, I'm of the opinion that a sideways movement at the tires (on dollies - i.e. no resisting force at all) would initially translate the rear link of the HA and thus get our rotational / translational sequence started.
I agree that, if there is no resisting force from the tires, then the TT is free to swing and the linkage will rotate/translate. However, as soon as the yaw angle is non-zero the tires will generate lateral force and will control the amount of yaw.
Ron
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guardrail
Lower 48 somewhere
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it works damn well
nuf said
2008 F450 CC Lariat White/Gold
B&W Hitch
Carriage Carri-lite CT36XTRM5
http://www.f150online.com/galleries/albumview.cfm?num=15052
Traded>>> 2003 F250 CC LB XLT 4x2
2005 Pilgrim 306RL-SS w/Hensly Arrow (sold 2-16-08)
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Ron Gratz
full time RVer
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TnAnFLA wrote:Ron, I think you've got it backwards.
Andy,
I'll accept that. That's why I said, "I think (but cannot prove)". This just demonstrates Milt's point that a person who does not own a HA should not comment about a HA.
Whether the struts are in tension or compression will not change the fact that simply snugging up the struts does not result in any net forces acting on the HA's side links and front link.
Quote:And if my recollection of physics is accurate (not a sure bet at all) the net force on the coupler/ball should be zero if both struts are of equal length. Both struts are "pushing" with equal force on opposite sides of the ball coupler.
The struts are at an angle to the TT's longitudinal axis. If the right strut is in compression, it will exert a force to the rear and to the right on the right side of the A-frame. The left strut would exert a force to the rear and to the left on the left A-frame. 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.
Ron
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tluxon
Kirkland, WA
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Milt, you may have missed the video I posted that Dave made for us a couple hundred posts back.
http://home.comcast.net/~tbluxon/Hensley_Motion_sm.WMV
I think it would also be helpful to review this post again which helps explain why the Hensley addresses sway more effectively than if it were locked. I think it also helps illustrate why the lateral reaction at the tires are an integral part of the Hensley's effectiveness.
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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tluxon
Kirkland, WA
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I also wanted to repeat the link to a couple video clips I combined from Hensley's marketing video. The first one shows the action of the hitch head when the angles are changing pretty slightly, like changing lanes on a highway. The second one appears to be taken in a parking lot with pretty tight turns.
http://home.comcast.net/~tbluxon/Hensley_Hitch_cam.WMV
I think the first one helps illustrate how much the hitch head translates from side-to-side at very slight angle changes.
BTW, I much prefer the black head to the orange head. Any chance they would sell it that way?
Tim
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bettered
UpCountry SC
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Joined: 07/26/2004
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We might ask Hensley, but I think the black head was an early model. I've not seen one like it. The newer hitches are much bigger as well. One of the things that drives them big is the position of the locking slots in the orange piece when the little gravity tab flips down to facilitate hookup. It also appears that they increased the distance between the rear (TT end) link pivot points and beefed up the links.
Ed
BetterEd
DW + 2 grandkids + Mini Schnauzer
2005 Chev 3500 Crew D/A 6.6L LLY, 6 x 6 DRW, 3.73
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Hensley + Prodigy
"Genius may have its limitations...." E. Hubbard 1856 - 1915
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Stressor
Whitefish Bay, Wisconsin
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tluxon wrote:Milt, if your proof is so good, why isn't anyone agreeing with it?
As far as the "principle of parsimony", the whole idea of being simple is to also be complete. Your proof has been anything but complete. For one, you've failed to explain how Hensley was able to make a pivoting pin that had the intelligence built into that only allows movement if initiated from the front "bar" but not the rear "bar".
Also, please explain why I've seen several Hensley owners comment that sometimes they see a slight wiggle from the TT but they couldn't feel it in the TV. Sounds like a great anti-sway device, but it sure doesn't sound like a "straight truck" to me.
Tim
Tim,
You have failed to grasp the simple mechanical linkage that the Hensley Arrow represents.
You are multiplying entities even as you write. 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.
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.
Milton Findley (and Kerene)
A small piece of my mind...
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Stressor
Whitefish Bay, Wisconsin
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Ron Gratz wrote:TnAnFLA wrote:Ron, I think you've got it backwards.
Andy,
I'll accept that. That's why I said, "I think (but cannot prove)". This just demonstrates Milt's point that a person who does not own a HA should not comment about a HA.
Whether the struts are in tension or compression will not change the fact that simply snugging up the struts does not result in any net forces acting on the HA's side links and front link.
Quote:And if my recollection of physics is accurate (not a sure bet at all) the net force on the coupler/ball should be zero if both struts are of equal length. Both struts are "pushing" with equal force on opposite sides of the ball coupler.
The struts are at an angle to the TT's longitudinal axis. If the right strut is in compression, it will exert a force to the rear and to the right on the right side of the A-frame. The left strut would exert a force to the rear and to the left on the left A-frame. 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.
Ron
Ron,
I meant to tell you, the struts can only be in compression, either less or more compression. There is absolutely no way to put one in tension, as it is a two part assembly, and simply falls apart.
When they are installed and correctly adjusted, they are in considerable compression.
They could be welded in place and it would make no difference in the operation of the hitch.
Once again, an entity has been multiplied.
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