Stressor
Whitefish Bay, Wisconsin
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I am with you until here:
"The HA's linkage does not provide a "rigid" connection at any angle, zero or otherwise. A heavier trailer and larger frontal area could cause a greater longitudinal "pulling" force on the linkage. However, the HA's linkage does not generate a moment in response to a longitudinal force. It only generates a moment in response to a lateral force."
The pendulum analogy works, but the hitch is not like a pendulum linkage in that the TT ends of the linkage can only move side to side in response to a lateral force applied along the side of the travel trailer.
How does the lateral force get transferred through the linkage from the travel trailer end to cause the VPP to move? And the answer is apparently that it does not, because the VPP does not move as a result of forces applied to the travel trailer. Where do the forces go? And how do they get there?
If I replaced the Hensley Arrow with a rigid linkage, call it a Pullrite, would the forces be distributed to the same places in the same manner?
Milton Findley (and Kerene)
A small piece of my mind...
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tluxon
Kirkland, WA
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Stressor wrote:...How does the lateral force get transferred through the linkage from the travel trailer end to cause the VPP to move? And the answer is apparently that it does not, because the VPP does not move as a result of forces applied to the travel trailer. Where do the forces go? And how do they get there? The VPP moves only as a result of a change in geometry. The lateral forces may or may not result in a change in geometry. With the Hensley, the vast majority of lateral force is reacted to by the tires of both vehicles due to the nature of the leverage of the linkage.
Stressor wrote:If I replaced the Hensley Arrow with a rigid linkage, call it a Pullrite, would the forces be distributed to the same places in the same manner? Not necessarily. The Hensley moves the point of leverage a certain distance forward of the trailer coupler, while the Pullrite moves the point of leverage to a point relative to the TV's rear axle. These points may - but most likely won't - be moved to the same location with each hitch.
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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Stressor wrote:...The pendulum analogy works, but the hitch is not like a pendulum linkage in that the TT ends of the linkage can only move side to side in response to a lateral force applied along the side of the travel trailer...
I think Ron was using the pendulum analogy to compare a conventional hitch that pivots at the ball coupler to a Hensley hitch which pivots at the point projected to by the side links (the VPP). Forget the lateral forces for a second and just think of the range of motion dictated by the geometry of the linkage. Does that help?
Tim
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Ron Gratz
full time RVer
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Joined: 12/27/2003
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Stressor wrote:The pendulum analogy works, but the hitch is not like a pendulum linkage in that the TT ends of the linkage can only move side to side in response to a lateral force applied along the side of the travel trailer.
The TT end of the linkage (the rear, upper, orange part of the HA) can move side to side and also can rotate (yaw). In fact, it only can move if it simultaneously translates and rotates. This is exactly what a pendulum does. As any given point on the pendulum rod moves to the side, the rod simultaneously changes its angle relative to vertical. If a lateral force is applied to the TT, the TT will swing to the side until the yaw angle is sufficient for the tires to develop an equal opposing force via their slip angles.
Quote:How does the lateral force get transferred through the linkage from the travel trailer end to cause the VPP to move? And the answer is apparently that it does not, because the VPP does not move as a result of forces applied to the travel trailer. Where do the forces go? And how do they get there?
See above. A lateral force imposed on the TT causes it to yaw relative to the direction of travel. This changes the angle between TT and TV and it is that change in angle which causes the VPP to move. The lateral force on the TT produces the change of angle and the change of angle causes the VPP to move. Of course, steering the TV to a different heading also will change the angle.
Quote:If I replaced the Hensley Arrow with a rigid linkage, call it a Pullrite, would the forces be distributed to the same places in the same manner?
If the PullRite's pivot point were at the same location as the HA's VPP and the effective tongue lengths were the same, the answer is Yes. The PullRite does not provide a "rigid" connection between TT and TV because it allows pivoting at its actual pivot point. The HA does not provide a "rigid" connection between TT and TV because it allows pivoting at its virtual pivot point. Both hitches provide a rigid connection (within the capability of the struts) at the ball coupler; but the pivoting which otherwise would occur at the ball simply occurs at a different location.
Ron
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Stressor
Whitefish Bay, Wisconsin
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"The TT end of the linkage (the rear, upper, orange part of the HA) can move side to side and also can rotate (yaw). In fact, it only can move if it simultaneously translates and rotates. This is exactly what a pendulum does. As any given point on the pendulum rod moves to the side, the rod simultaneously changes its angle relative to vertical. If a lateral force is applied to the TT, the TT will swing to the side until the yaw angle is sufficient for the tires to develop an equal opposing force via their slip angles."
The orange head on my Hensley is fixed into position and never, ever moves. Two great big iron bars keep it from moving at all. There is no movement except through the linkage.
Tim,
"The VPP moves only as a result of a change in geometry. The lateral forces may or may not result in a change in geometry. With the Hensley, the vast majority of lateral force is reacted to by the tires of both vehicles due to the nature of the leverage of the linkage."
My point exactly. The leverage of the linkage prevents a change in geometry.
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Ron Gratz
full time RVer
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Quote:(with addition)
The orange head on my Hensley is fixed into position and never, ever moves relative to the TT's tongue. Two great big iron bars keep it from moving at all. There is no movement except through the linkage.
Milt, If you add the phrase in red, the statement is correct. I am talking about the movement of the orange head relative to the lower, front, black portion of the hitch. The linkage allows the orange part to move about 5" to either side relative to the black part.
From the Hensley patent document
"A hitch assembly for coupling a trailer to a tow vehicle, said hitch assembly comprising: a first pivot member adapted to be attached to the tow vehicle; a second pivot member adapted to be attached to the trailer and being offset vertically with respect to the first pivot member; a pair of connecting links extended between the first and second members with each link being pivotally connected to the first member at a first pivot axis and also to the second member at a second pivot axis such that the second member may swing from a normal position to a substantially angulated position without the links and members interfering with each other,..." (bold added for emphasis)
Ron
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tluxon
Kirkland, WA
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Stressor wrote:Ron Gratz wrote:The TT end of the linkage (the rear, upper, orange part of the HA) can move side to side and also can rotate (yaw). In fact, it only can move if it simultaneously translates and rotates. This is exactly what a pendulum does. As any given point on the pendulum rod moves to the side, the rod simultaneously changes its angle relative to vertical. If a lateral force is applied to the TT, the TT will swing to the side until the yaw angle is sufficient for the tires to develop an equal opposing force via their slip angles.
The orange head on my Hensley is fixed into position and never, ever moves. Two great big iron bars keep it from moving at all. There is no movement except through the linkage.
I don't think Ron was trying to imply that the orange head moved - only that the linkage on that side (the trailer side) of the Hensley could move side to side while rotating [added] (angulating) with respect to the TV. I don't believe he's saying the rear link ever rotates with respect to the TT.
Stressor wrote:Tim, tluxon wrote:
The VPP moves only as a result of a change in geometry. The lateral forces may or may not result in a change in geometry. With the Hensley, the vast majority of lateral force is reacted to by the tires of both vehicles due to the nature of the leverage of the linkage.
My point exactly. The leverage of the linkage prevents a change in geometry. I hope what you mean by "prevents" is "greatly resists". The end result is that any change will be virtually imperceptible, but it is possible for a significant lateral force to create a slight change in the geometry of the linkage which indeed would result in a change in the angle between the TT and TV. The magnitude would have to be very large and it would still result in an extremely small angle change and leverage against the TV. It would be virtually impossible for the TV to react in a way that could cause oscillation, so the driver will never be able to detect any change.
[added] Now, if you take the tires out of the equation by hanging the vehicles into a position much like a clock pendulum, the motion - and resultant continual change in geometry - is quite free. It just simulates the motion of a much longer pendulum due to the linkage. Make sense?
Tim
* This post was
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edited 05/19/05 09:10pm by tluxon *
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Ron Gratz
full time RVer
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tluxon wrote:I don't think Ron was trying to imply that the orange head moved - only that the linkage on that side (the trailer side) of the Hensley could move side to side or rotate. I myself am not sure that the rear link ever rotates with respect to the TT.
Oh, yes he was. The orange head is, in fact, the rear link; and the TT tongue is rigidly connected to it via the ball coupler and the struts. The rear link and the two side links can, and do, translate and rotate realitive to the front link (which is the black portion of the hitch). The rear link does not move relative to the TT, but it does move relative to the TV.
Ron
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tluxon
Kirkland, WA
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Ron Gratz wrote:tluxon wrote:I don't think Ron was trying to imply that the orange head moved - only that the linkage on that side (the trailer side) of the Hensley could move side to side or rotate. I myself am not sure that the rear link ever rotates with respect to the TT.
Oh, yes he was. The orange head is, in fact, the rear link; and the TT tongue is rigidly connected to it via the ball coupler and the struts. The rear link and the two side links can, and do, translate and rotate realitive to the front link (which is the black portion of the hitch). The rear link does not move relative to the TT, but it does move relative to the TV.
Ron I edited my comment in the original post sometime between when you started to respond and the time you posted the above. It now reads,
tluxon wrote:I don't think Ron was trying to imply that the orange head moved - only that the linkage on that side (the trailer side) of the Hensley could move side to side while rotating (angulating) with respect to the TV. I don't believe he's saying the rear link ever rotates with respect to the TT. I think we're essentially saying the same thing - just in different ways.
Tim
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Ron Gratz
full time RVer
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Stressor wrote:
My point exactly. The leverage of the linkage prevents a change in geometry.
The linkage does not prevent a change in geometry. The linkage does not prevent the TT from swinging behind the TV. It is only the lateral forces on the TT's tires (and inertial effects) which prevent the TT from swinging. If a gust of wind hits the side of the TT, it will swing to a new yaw angle. When the wind goes away, the TT will swing back. The linkage prevents neither swinging to nor swinging fro. However, the effective lengthening of the TT tongue will have some effect on the period and amplitude of the swing.
Ron
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