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Old 08-12-2013, 08:22 PM   #43
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I have seen the tail wag the dog!

Trailers will not travel in a straight line by themselves because they have either a single axel or multiple axels close together. If your trailer disconnected from the tow vehicle it would not continue to travel in a straight line. The only thing keeping the trailer straight is the tow vehicle and the hitch. A car or truck on the other hand has 4 wheels spaced apart and will stay under control on it's own.

We had the tail wag when I was a kid, towing a small popup with a minivan (appropriate combination ) no sway control or weight distribution, my father would lift the tong on to the ball with one arm. We had brought firewood loaded at the front of the trailer (back when you were allowed to) and burnt it all. On the way home we had no weight at the front of the trailer. At 100km/h the tong would sway sided to side pulling the back of the van with it, almost loosing control.

I saw the exact same issue with improperly loaded single axel utility trailers behind a Chevy 1500, and another time a Ford full sized van. We were following in another vehicle and saw the trailer push the trucks almost around in a circle. It's pretty scary seeing the side of a van in front of you at 100km/h

We have not had this kind of issue with our Airstream because we have a properly loaded trailer and properly set up hitch.
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Old 08-13-2013, 05:36 AM   #44
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Lego Hensley Arrow Model - YouTube

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Originally Posted by andreasduess View Post
That's the point. With a similar amount of force applied, the Hensley setup doesn't move.
The point is.....it's easy to see in the video there was not a similar amount of force applied.
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Old 08-13-2013, 05:42 AM   #45
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The point is.....it's easy to see in the video there was not a similar amount of force applied.
Or alternatively, that the setup works?
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Old 08-13-2013, 07:14 AM   #46
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Always good to have a skeptical eye....we all have sides we settle on or choose. Another persons perspective is valuable.. My Pop told me, "You won't be a failure in life. Either you will be a wonderful example or terrible,bitter warning."

Gee, thanks, Pop!

The basic demonstration/experiment was flawed from my casual observation. Agreed.

To prove the point, there is no calibration or measurement of the rotational forces applied by the presenter. I. e.; a torque meter to measure the twist applied on the Z or yaw axis. There should also have been measurement if sideways forces on the trailer axle.

So, i dug out my sons bucket of Legos, built my own and attempted so that u could experience the experiment myself (bitter warning/hold my beer)

Results I personally witnessed.....among many but not a complete list:

- PP style hitch wanted to force the trailer axle and wheels Sideways, not rotationally, unexpected
- standard coupling was a simple lever and axle arrangement allowing the trailer axle and wheels to pivot, as expected.
- PP hitch required significant force to move trailer axle and wheels sideways
- standard hitch simply rolled tires (and caused alignment change in TV to trailer alignment (sway))
- When axle and tires change direction that us called "steering". That steering of the axle and wheels by the standard hitch will cause the trailer to steer in direction aimed.
- I presume, if the trailer axles are pointed in one direction, the trailer would generally go that way. If that ludicrous guess is maintained then the trailer would move in the direction aimed. This would continue until the misalignment if TV to trailer is resolved. During that time you have mass and inertia and acceleration causing the misalignment to do unusual things to your Legos. That is what we refer to as "sway". It is like "The Narrows Bridge" or "Galloping Gertie" I believe it was called, to develop an harmonic oscillation. No one believed possible at the time, but they didn't have Legos Sway can be as sudden and more violent due to the lighter weights involved
- in PP hitch, most of the initial misalignment of RV and trailer is damped by the trailer tires. You STILL have the same forces at work, only the harmonic doesn't have a chance to multiply

If I lift just the TV tires and move sideways, the PP Legos try to stay in alignment.

If I do same with standard hitch, the trailer just wiggles freely at the hitch point and the trailer wheels pointing in the direction of the rear bumper of TV movement.

When I find some LT tires for my sons' Lego Segway I may reattempt my flawed test. Now who has my beer?
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Old 08-13-2013, 11:07 AM   #47
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Quote:
Originally Posted by LFC View Post
Lego Hensley Arrow Model - YouTube



The point is.....it's easy to see in the video there was not a similar amount of force applied.
Hi did you this video ?
http://ProPride 3P Hitch Lego Model - YouTube
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Old 08-13-2013, 11:55 AM   #48
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Originally Posted by LFC View Post
Lego Hensley Arrow Model - YouTube

The point is.....it's easy to see in the video there was not a similar amount of force applied.
I agree. To my eyes, it looked like the guy's hand moved much more forcefully when demonstrating the non-Hensley model. I wonder whether that was intentional or a subconscious thing?? As an MIT student, you would think he'd have access to some sort of tool (not his hand) that would input the same exact signals on both models. Then again - we're talking about Legos here :-)

I agree with his conclusion and love the demo but agree its a little flawed.
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Old 08-13-2013, 11:56 AM   #49
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Holy shnikes, CWF! That was fun to read!! Now we just need YOUR video!! :-)
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Old 08-13-2013, 12:53 PM   #50
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Holy shnikes, CWF! That was fun to read!! Now we just need YOUR video!! :-)
Agreed. That was AWESOME. I love pop's wisdom too.
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Old 08-13-2013, 02:32 PM   #51
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Geez I thought this was about trailer sway and NOT ANOTHER PROPRIDE COMMERCIAL.
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Old 08-13-2013, 02:52 PM   #52
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Geez I thought this was about trailer sway and NOT ANOTHER PROPRIDE COMMERCIAL.
Some asked if the tail wags the dog, and someone said no if you have a Hensley/ProPride, and someone said no way, and someone said no sway, and someone asked how can that be.

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Old 08-13-2013, 06:47 PM   #53
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Quote:
Originally Posted by SteveSueMac View Post
I agree with his conclusion and love the demo but agree its a little flawed.
Steve, Benjamin Hu's Lego Hensley Arrow is more than a little flawed. It is significantly flawed, and flawed in favor of the HA versus the conventional hitch.

If we assume the model TV represents a wheelbase of 130" (e.g. a Suburban), the model of the HA would represent a Virtual Pivot Point located about 26" ahead of the Suburban's rear axle instead of about 25" behind the rear axle where it should be.
This means the model TV is much less influenced by lateral force applied via the Lego HA hitch than a real TV would be.

The ball of the "conventional" hitch scales to be about 140" behind the Suburban's rear axle versus an actual distance of about 65".
This means the model TV is much more influenced by lateral force applied via the Lego"conventional" hitch than a real TV would be.

The ball-to-axle distance for the TT towed by the Lego HA scales to about 90" -- which would correspond to a TT with a body length of about 7'.
The ball-to-axle distance for the TT towed by the Lego "conventional" hitch scales to about 175" -- which would correspond to a TT with a body length of about 18'.
Again, this scaling flaw gives the HA hitch a very large perceived advantage over the "conventional" hitch.

The biggest misrepresentation in the video is the act of simulating a yaw-axis torque applied to the Lego trailer.
And, I'm not talking about whether Mr. Hu applied a greater amount of twist when the TT was connected with the "conventional" hitch.

The misrepresentation is the fact that a real TT is not subjected to a pure yaw-axis torque.
A real TT is subjected to lateral forces which tend to make the TT pivot about its pivot point -- the ball, for a "conventional" hitch, and the VPP, for a HA.
Furthermore, when the TT is moving down the highway, there is no lateral resistance provided by its tires unless the TT swings so that the tires are pointed at an angle to the direction of travel.

Applying a yaw-axis torque to the model TT is an unrealistic simulation of how the HA (or PP) responds in a sway event.
A realistic simulation would be to have the TT tires on a friction-free surface, and load the TT with a lateral force instead of a "twist".

Given the right external loading, a TT will exert a lateral force on the rear of the TV.
With a "conventional" hitch, the force will be exerted on the ball which might be about 65" behind the TV's rear axle.
With a HA or PP, the lateral force will be exerted at the VPP which might be about 25" behind the rear axle.
The shorter moment arm means that less steering torque will be imposed on the TV when the TT is connected via a HA or PP.
Less steering torque means there is less tendency for the driver to overcorrect, and that means there should be less likelihood of loss of control.

The concept is pretty simple, and it has not been simulated correctly by any of the video models I've seen.

Ron
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Old 08-13-2013, 07:18 PM   #54
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Originally Posted by Ron Gratz View Post

The concept is pretty simple,

Ron

Ron - I totally respect your knowledge and appreciate all the help you've given me in and out of the forum. Please don't take this wrong because it says more about my puny mind than anything about you...but I nearly fell out of my chair when following a near doctoral dissertation on the flaws in the Lego model, you said the above snippet.... :-D

Love it!!! :-)
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Old 08-13-2013, 07:26 PM   #55
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Geez I thought this was about trailer sway and NOT ANOTHER PROPRIDE COMMERCIAL.
Wonder how much hype you have to "sway" to get a discount ?

On the flip side I'm sure it's a great hitch....

I'm guessing the Leg O video was for the "simple" minded customers.
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Old 08-13-2013, 07:33 PM   #56
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Quote:
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Wonder how much hype you have "sway" to get a discount ?

On the flip side I'm sure it's a great hitch....

I'm guessing the Leg O video was for the "simple" minded customers.
Thanks for noticing LFC! Bless you too!
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