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Old 04-14-2019, 04:46 AM   #155
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Just ordered a PP a few minutes ago. Sean seems like a nice guy, glad to do business with him

As to the U-Haul video, there is an interesting one that shows a simulation of what the PP does.


Realize that all of the dynamics involved in trailer sway are very complex, but at the core, it is an undamped harmonic oscillation that runs away. It is highly dependent on speed and loading (CG). Btw the pdf from Delphi is not really applicable to this conversation as he was designing an asymmetric braking system and needed a test rig he could force to misbehave. He also stated that CG is a major factor and adjusting it fore and aft had significant effects on stability.
The equations used in the pdf for understeer gradient and sway damping ratio are the same regardless of trailer type. So yes it is applicable to stability. Stability is dependent on Inertial (mass), Geometric (dimensions), and axle cornering stiffness properties of TV and TRL.
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Old 04-14-2019, 05:24 AM   #156
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The equations used in the pdf for understeer gradient and sway damping ratio are the same regardless of trailer type. So yes it is applicable to stability. Stability is dependent on Inertial (mass), Geometric (dimensions), and axle cornering stiffness properties of TV and TRL.
And has nothing to do with what brand hitch you are using.

Bob
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Old 04-14-2019, 06:17 AM   #157
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You are correct since stability should be established before any WDH and sway control is added.
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Old 04-14-2019, 07:46 AM   #158
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.
Stability is dependent on Inertial (mass), Geometric (dimensions), and axle cornering stiffness properties of TV and TRL.🤓


No mention of the hitch...🤔
Yes, you can do everything you said but you still won't PREVENT sway from happening.
PPP prevents the onset.

Bob
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Old 04-14-2019, 09:42 PM   #159
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Just a word of caution, the equations in the Delphi pdf are making some assumptions which allow us to infer what the dynamics are, not guarantee what will happen. It also ignores friction damping, WD and many other factors.
"Even for a specific vehicle-trailer combination, most of these
parameters can be greatly altered by changing parameters
that are in control of the user, such as weight distribution
or tire type and tire pressure." -Delphi article

I think the basic dynamics analysis would need to be redone given the changes the PP hitch introduces into the system as far as the kinematics go. This analysis also assumes constant speed for the dynamic analysis and is mainly focused on if the braking system which is being developed is actually working as intended to stop unwanted harmonics in the system.

It is a good read and has some useful information but it should not be applied too broadly with its conclusions. Sortof like that a little bit of knowledge can be a dangerous thing, lol.

The take away from the Delphi paper, as I see it, is to watch your loading and CG, have sufficient damping or the ability to apply variable braking (like the braking system they designed).

Alternatively, you can bypass those particular dynamics altogether with a system like PP or Hensley. Lots of options for lots of budgets and risk tolerances. There is no "right" answer to these questions but a whole lot of next best solutions using knowledge and wisdom.
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Old 04-15-2019, 03:16 AM   #160
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Those equations are used by engineers to design and test vehicles and are not specific to this one paper. It relies on the tires and proper loading of both TV and TLR to PREVENT sway which happens when critical speed is above travel speed. The PP/HA is still a WDH and will reduce rear axle cornering stiffness like any other especially when high amounts of tension is used. Like it or not that will effect static stability of the combination since the rear tires now become the weak point of the system.
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Old 04-15-2019, 05:40 AM   #161
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What you say is just screen BLITHER...it's what I DO that counts, and what I do, I do without any SWAY...I'm no enginear, I just play with 'em on the innerspace, keeps me SMILING.😂

Bob
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Old 04-16-2019, 12:26 AM   #162
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I'm going to ask a question, do you happen to be an engineer. I only ask because you seem to have a good grasp of the mechanics involved and if you have that training for a resource and that kind of deep of knowledge I want to respect it. There is so much misinformation as well as people trying to prove they are right online that sometimes the message gets lost in the shuffle. The goal is for people to be safe! Do I know all the answers, nope, but I know parts. I'm no expert in this field and if you are I will defer to your knowledge
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Old 04-16-2019, 03:22 AM   #163
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No I am not an a formally educated mechanical engineer and have never claimed to be, just have a strong desire to understand how and why things work. Neither do I have a degree in computer science but that’s the field I do my work. If anything, I hope to encourage others to do they’re own research and educate themselves on the subject and use solid facts to make decisions.
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Old 04-16-2019, 05:43 AM   #164
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I can respect the desire to learn and educate yourself! More people should follow that example! I don't work as a Mechanical Engineer either, but I was trained as one (Mechanical Design concentration but I work as an accountant now though). There are many nuances that can be left out of autodidactic learning as I am constantly finding in my quest to play with computers.

Equations in engineering which model the physical world are just that, models. They are by necessity simplified (to make the math easier, or more understandable, or faster, etc) as they are a compromised representation of the physical world. A paper that describes a problem and specific possible solution and then applying that conclusion over a broad topic is asking for trouble. The subset of the problem is not the whole problem. Trailer sway is a problem, and a potentially catastrophic one (as almost all uncontrolled harmonic systems are) but it is only one subset of the problems out there, and there are many ways to solve each problem individually (which may introduce their own problems, lol).

One other thing that is interesting in mechanical engineering and the related physical engineerings (Structural, Aero, etc) is the factor of safety. it's when we do the calculations to the accuracy desired and with the proper sets of assumptions (material, forces, temp, loads, vibrations, etc) and get a number X saying this is what we think is needed to satisfy the design criteria. At that point, one would think the job is done, but you would be vastly wrong, lol.

ASME (American Society of Mechanical Engineers) steps in and says we should use a factor of safety to account for the things that we don't know about or can't control for cars it's typically 3.0, though some parts I'm sure are higher and some lower. Selecting this number is complex in itself and the lawyers and accountants should have a say too because if the part gets too expensive to make or it is too dangerous that it will result in GBH a redesign is in order.

Basically, it is a compromise to design anything because we are constantly pushing the limits of the materials we design with. Composite structure analysis and the Matrices to transition loads through the layers of the structure were a real eye-opening experience (fun too though), lol.
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Old 04-16-2019, 06:03 AM   #165
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No I am not an a formally educated mechanical engineer and have never claimed to be, just have a strong desire to understand how and why things work. Neither do I have a degree in computer science but thatís the field I do my work. If anything, I hope to encourage others to do theyíre own research and educate themselves on the subject and use solid facts to make decisions.
I'm shocked. I mean, when you wholeheartedly agree with another poster that claims the hitch industry has conspired for over a half century to sell us big heavy, complicated, expensive hitches that do nothing to help us safely tow, I assumed you were speaking from a highly technical and educated background.
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