Stressor
Whitefish Bay, Wisconsin
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Looks good to me Burbman, but then, I am a psychologist... ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/biggrin.gif "biggrin")
This is a very informative thread, and I really like the diagrams. They make the dynamics easier to understand, and beat my graph paper drawings.
Milton Findley (and Kerene)
A small piece of my mind...
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Claude B
Montreal, Canada
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Quote:Claude B: I didn't suffer any diff. Problems, altho I worried about and expected it. I don't understand what you mean that the pivot point was the same as a standard hitch with weight dist. bars. Jack
Jack, you need a pivot point between the TT and the TV, and the hitch ball was the pivot point. Correct me if i'm wrong but the hitch head and the wd bars where quite the same as any standard wd hitch that we use now (Reese, Draw-Tite, Eazy-lift ect.)
Claude
2013 Gulf Stream VISA 19ERD
VW Touareg TDI 2013
VW Passat 2012 TDI
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tluxon
Kirkland, WA
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You've got it dead on, BurbMan. I love it when a marketing guy uses the term, "moment arm".
For all practical purposes, every horizontal force (unless it's directed through the longitudinal axis of a straight TV/TT combination) has a moment arm acting to rotate either the TV or the TT. Any of these attempted rotations can disrupt the equilibrium of the "hinge" at the hitch, resulting in a pendulum-like horizontal oscillation between the TV and TT. This is good for a fish wanting to swim fast, but very bad for a TV/TT combination.
Conventional hitches depend on friction and/or long TV wheelbase and/or minimal TV overhang to fight off these attempted oscillations while the Hensley does it (as does the Pullrite) by reducing the lever on the TV by some 4 feet. It's a bit like being asked to tighten a nut with your fingers instead of with a long wrench.
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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Ron Gratz
full time RVer
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BurbMan wrote: With the Hensley, the same lateral force is still present, and with the same magnitude, but the VPP created by the 4-bar linkage effectively moves the force forward in the TV, eliminating the leverage of the moment, and greatly increasing the TV's ability to resist the force.
How'd I do guys?
Don
Don,
I would give you a B+. The HA does not eliminate the moment arm unless you have a TV with an overhang of around 30". In general, the HA significantly reduces the moment arm by projecting the pivot point a fixed distance (lets assume 47" for the time being) forward from the ball connector.
For example, lets assume that, for your rig with a conventional hitch, the TV rear axle to ball distance is 65". Therefore, the conventional hitch would have a moment arm of 65". Lets also assume that installing a HA would add and extra length of 12". This means the axle to ball distance with the HA would be 65+12 = 77". Now if the HA projects the point of application of lateral force forward by 47", the moment arm would be 77-47 = 30". The moment arm has not been eliminated, but it has been reduced from 65" to 30" – more than 50%. Fill in the correct numbers for your rig and you can do the calculations.
But, as the telemarketers say, Wait! There’s more! At the risk of giving away some of the plot, you soon will read that the HA also reduces the magnitude of the lateral force relative to that which would be exerted by a TT coupled with a conventional hitch. So, the reduction in length of the moment arm combined with a reduction in magnitude of the effective lateral force produces a compound effect on the moment which is trying to steer the TV. Stay tuned.
Ron
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BurbMan
Indianapolis, IN
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Well, I spent my first 3 semesters at college (Purdue) thinking I wanted to be an engineer....in fact when I took differential calculus in my 3rd semester, I was done with the math requirement for a degree, but I couldn't get my arms around chemistry and physics. Moved on to a business degree....every once in a while I wish I would stuck with engineering!
Ron, thanks for the clarification, and I guess I meant to say that it reduces the moment arm, not eliminates it. This is all pretty straightforward, but what's really interesting to me is how you are going to demonstrate that the HA actually reduces the lateral force....I guess I'll have to stay tuned...
Don
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tluxon
Kirkland, WA
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I'm not sure if this is what Ron is getting at, but in very simple terms, lateral forces are reduced to a moment about the trailer's axles, which must be reacted on by another moment represented by a force at the tongue coupler with a moment arm that is the distance from the center of the trailer's axles to the coupler. The Hensley makes this moment arm longer, thus reducing the force at the end of it.*** It's this now-reduced force that acts laterally on the TV. But remember that this lateral force acting on the TV has a much shortened lever to work with on the TV due to the Hensley.
Thus the effect of attempted oscillation is reduced by magnitudes - twice.
*** A moment is a force multiplied by a distance. For any given moment, increasing the force decreases the distance and increasing the distance reduces the force.
Make sense?
Tim
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BurbMan
Indianapolis, IN
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Not quite....mathematically, you are right, moment = force x distance. BUT, increasing the distance only lessens the force required to produce the same moment. If we assume that the crosswind is blowing at 20mph, changing the length of the lever is not going to make the wind blow slower. Further, we can assume that the wind gust exerts pressure at all points along the side of the trailer, not just at the coupler, so theoretically, there are an infinite numbers of points where force is applied, each with corresponding moments from the TT axle.
Of course, the same wind is applying its force to an infinite number of points along the same side of the TV also, so does that produce a series of counter moments?
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tluxon
Kirkland, WA
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BurbMan wrote:Not quite....mathematically, you are right, moment = force x distance. BUT, increasing the distance only lessens the force required to produce the same moment. Well, if I'm the TV and I have a longer lever to work with against the TT's moment, I'm not going to need to apply as much force to counter that moment. Follow?
BurbMan wrote:...If we assume that the crosswind is blowing at 20mph, changing the length of the lever is not going to make the wind blow slower. No, but it's going to make it easier for the TV to counter the composite moment it creates.
BurbMan wrote:...Further, we can assume that the wind gust exerts pressure at all points along the side of the trailer, not just at the coupler, so theoretically, there are an infinite numbers of points where force is applied, each with corresponding moments from the TT axle. Yes, and that's why you want to reduce all those moments to a single composite moment in order to know the reaction at the coupler. Remember the old rule, the sum of the moments must equal zero?
BurbMan wrote:...Of course, the same wind is applying its force to an infinite number of points along the same side of the TV also, so does that produce a series of counter moments? Dealing with the wind effect on the TV is a much more complex issue due to the fact that the front axle has turning wheels attached, but the TV is not affected nearly as much by the wind as the TT. You want to break the problem down to the simplest terms possible, so I would think it sufficient to concentrate on the lateral force the TV needs to adequately react to a given lateral force from the TT.
Tim
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LAdams
Northern Illinois
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When you guys get through with this GREAT THREAD, I'm gonna see if we can make it a "sticky" in the TT forum...
NICE JOB GUYS!!!
Moderator - TT Forum
ON EDIT: When you guys are done, perhaps one of you can compile the thread into a logical sequence that we could archive into a sticky...
Les
* This post was
edited 05/17/05 02:04pm by LAdams *
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RoarinRow
Elk Grove, CA.
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It's a very interesting thread to say the least. From a laymen's prospective we were immediately impressed by the overall design of the Hensley. People walk up to it and ponder on the mechanics of it, which I could not begin to describe.
The testimonials on the video were convincing, especially when the older woman cried about how safe she felt. We spoke to other Hensley owners (who also had other types of hitches prior) and they too could not praise the Hensley enough.
As first time RV'ers we don't/didn't want to experience anything less than what the Hensley claimed.
It may not be for everyone, but for us, who are close to the maximum towing capacities (TT and TV), we wanted what we felt was going to be the best. As far as how it works, well . . .we're just concerned that it does work.
TV - 2002 1500 Chevy Avalanche 5.3l 4x4 4.10
TT - 2010 187 Cikira Classic Cruiser
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