Friction sway control...worthwhile?

[ROBERT CROSS]

^
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
🇺🇸

[RedBearded]

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

[Profxd]

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.

[RedBearded]

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.

[smithcreek]

Originally Posted by Profxd

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.

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.

[Collyn]

Originally Posted by RedBearded

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.

With respect I think it needs emphasising that the basic issue is an overhung hitch that introduces a 180 degree phase shift with the rigs momentum fuelling what rapidly becomes a positive feedback loop.

May I just add that a few posts re friction sway control overlook that frictional forces are constant but the forces involved increase with the square of the speed. They thus work well at low/medium speed but their effect is a mere 1% or so by 60 mph.

I am in Australia - where the caravan industry (and many owners) seem to belief they are immune to Newton's more basic laws - and have trailers that are far heavier than whatever pull them. The main stability issue, however, is their length - not weight.

(We await the results of your Nov election with a mix of trepidation and interest!).

Collyn