Eliminate WD issue with water!

[Road Ruler]

Good info Terry. That explains it. thnxs

[gamana]

Originally Posted by overlander63

Many of them were "fixed" by Airstream after this tendency was discovered. The one I towed had not been retrofitted with the "fix". The "fix" is to weld several hundred pounds of steel into the tongue of the trailer. I didn't go into that because it was not relevant to the topic.

Quite relevant as Airstream did exactly the opposite of my silly idea by adding weight to the tongue instead of removing it.

Another question: does the amount of axles on the trailer reduces sway?

[overlander63]

Originally Posted by gamana

Quite relevant as Airstream did exactly the opposite of my silly idea by adding weight to the tongue instead of removing it.

Another question: does the amount of axles on the trailer reduces sway?

Single axle trailers will tend to sway more than multi-axle trailers.

[markdoane]

Axles don't reduce sway. Tire sidewall stiffness reduces sway.

More axles = more tires = more sidewall stiffness = less sway.

[gamana]

That's what I thought. I always wondered why trailers were not built with two axles far apart with the front axle built on pivot (like a car). It would reduce the sway and lighten the tongue, no?

[2airishuman]

Originally Posted by markdoane

Axles don't reduce sway. Tire sidewall stiffness reduces sway. More axles = more tires = more sidewall stiffness = less sway.

so 6 tires on ONE axle = 6 tires on 3 axles, in relation to sway control or stability?



cheers
2air'

[Airstream01]

Go big or go home. All these gimmicks you're thinking of will cost more in the long run and will leave you upside down in a ditch in short order.

Do it right or not at all.

[gamana]

Originally Posted by Airstream01

Go big or go home. All these gimmicks you're thinking of will cost more in the long run and will leave you upside down in a ditch in short order.

Do it right or not at all.

Well, you view it as gimmicks. I view it as thoughts. I am not an engineer, builder or stunt man, I certainly don't like flipping into ditches and, as a matter of fact, I know just about nothing about sway. I would therefore use, like everyone else, a good WD, sway control and TV to tow an AS.

BUT, going back to concepts, considering that all objects in motion tend to sway from outside forces, it is obvious that some objects do better than others in controlling sway. A car, for example, is subjected to the same outside forces than the trailer but it handles sway better. You could say that the car is smaller (lower center of gravity) than the trailer but even if you take a bus the same size as the trailer, it will still handle better.

I could be completely wrong but my guts tell me that the tires in each corner of the car/bus are the main factor as to why the sway is controlled.

Now, why would the principle not be applicable to a trailer?

go ahead. bury me.

[tpi]

I believe one of the reasons axles/tires are located close together on a trailer is they would simply scrub and scuff way too much in turns if they were located out at the corners. A car's front wheels steer so that isn't a problem.

[gamana]

Originally Posted by tpi

I believe one of the reasons axles/tires are located close together on a trailer is they would simply scrub and scuff way too much in turns if they were located out at the corners. A car's front wheels steer so that isn't a problem.

true, unless the front axle of the trailer is also on a pivot, similar to those big farm trailers.

[hampstead38]

There are trailers with wheels at "the four corners." In this country, we call them "hay wagons." The small version are called "little red wagons." They both have front wheels that steer.

As for your theory of sway, motorcycles can be extremely stable and they only have two wheels. I'm also going to disagree with Mark Doane. The flex of tire sidewall can be important for vehicle handling on corners, but when it comes to travel trailers, properly balanced and aligned running gear is far more important.

A properly aligned, balanced and loaded single-axle trailer correctly hitched can certainly pull (and track) better than a poorly aligned, unbalanced and improperly loaded and/or hitched dual axle trailer. Dual axles are more forgiving because of the additional friction between the road and the tire. Try this. Take a roller skate. With only two wheels on the ground, roll it in an "S" path. It moves back and forth pretty easily. Now follow the same path with all four wheels on the ground.

Most vehicles have all kinds of improvements that trailers don't have, like independent front (and rear) suspensions. If you want some insight into why trailers sway, I'll let you take a spin in our '66 Dodge D200 with single beam axle front suspension.

Here's the thing. What you see on the road today, trailers and vehicles, represents the cumulative experience of billions of miles traveled and the thoughts of some of the finest engineering minds the world... and a heckuva lots of compromising to make things affordable. I appreciate the brainstorming, but there's some common sense reasons why travel trailer have the current hitch/ball setup with tires that don't steer. Again, try a practical experience. Put your kid in a little red wagon and pull him (or her) over a rough surface. Because the wagon wheels can turn, they do (even if you are trying real hard). When the wheels turn, the wagon's momentum shifts and you have real sway on your hands.

Now, if you made a travel trailer with eight or ten axles, it probably wouldnt sway much (particularly if everything was aligned), but I wouldn't want to turn it often.

[flmgrip]

Great idea, go right ahead... I can't believe not one trailer manufacturer has thought about this...

[ROBERTSUNRUS]

Hi, I do not recommend this or suggest doing it, but I think you would be much better off installing a water tank on the front bumper of your tow vehicle for the added weight needed to keep the front wheels on the ground. This is still crazy, but to me, makes a lot more sense than your idea of weight in the rear of the trailer.

Note: I would never do this, but this thread needs someone to stir the pot.

[Foiled Again]

Odd no one mentioned fifth wheels or the Draw tite hitch that basically puts the pivot point under the tow vehicle's rear axle.

Just wanted to toss a bit of petrol on the fire.

Paula

[rangebowdrie]

Back on page two, (I think), of this thread, Jammer hit the nail on the head, with just three words; "moment of inertia". This concerns yaw around the polar axis, and the stability is enhanced when the moments are asemmetrical in relation to the trailer axle(s).

[barts]

Here's an interesting link; I took several classes during graduate school from the author, and was the teaching assistant one spring in his class in vehicle stability back in the 80s.... Equation 5.44 on page 95 is relevant...

- Bart

[overlander63]

Originally Posted by barts

Here's an interesting link; I took several classes during graduate school from the author, and was the teaching assistant one spring in his class in vehicle stability back in the 80s.... Equation 5.44 on page 95 is relevant...

- Bart

Thanks for the link, I've bookmarked it for future perusal.

[bryanl]

The link about the single degree of freedom model is a common misdirection in these discussions. It's failure is that it assumes an infinite mass tow vehicle with rotation around the hitch point.

Trailer sway is most often rotation about the trailer's center of mass pushing a limited weight tow vehicle around.

There are two key points about trailer sway that need emphasis IMHO. One is that it cannot be eliminated but only reduced to something comfortable. The other is that it is the driver response that is often the most significant factor in escalating episodes. That is due to the fact that most hitches tend to promote oversteer and many drivers don't compensate properly.

As for 'wheels on the corner' trailers, I saw a bunch of them heading up a canyon while at a rally last year -- sheepherders on their way to shear a flock. For most of us, the simplicity of a centered axle trailer is good enough.

As for size, some of the best sway handling advice I have seen is from tent trailer owners. Smaller trailers can be quite active but they don't have the weight to really push around the tow vehicle.

[barts]

Originally Posted by bryanl

The link about the single degree of freedom model is a common misdirection in these discussions. It's failure is that it assumes an infinite mass tow vehicle with rotation around the hitch point.

Trailer sway is most often rotation about the trailer's center of mass pushing a limited weight tow vehicle around.

There are two key points about trailer sway that need emphasis IMHO. One is that it cannot be eliminated but only reduced to something comfortable. The other is that it is the driver response that is often the most significant factor in escalating episodes. That is due to the fact that most hitches tend to promote oversteer and many drivers don't compensate properly.

As for 'wheels on the corner' trailers, I saw a bunch of them heading up a canyon while at a rally last year -- sheepherders on their way to shear a flock. For most of us, the simplicity of a centered axle trailer is good enough.

As for size, some of the best sway handling advice I have seen is from tent trailer owners. Smaller trailers can be quite active but they don't have the weight to really push around the tow vehicle.

You'll note that the text starts with a single DOF model; the final analysis I referred on on page 95 is a three DOF approach, and includes the effects of tongue length, CG position, speed, polar moment and damping on stability.

I completely concur with your comments regarding driver input; I've driven rigs that demonstrated complete phase reversal on input in that counter-steering produced more pronounced sway rather than reducing the problem; if one steered with the sway it went away.

Of course, a more complete analysis would include any roll steer due to trailing axles; I've not seen such in the literature in casual search, however. It's clear that the dynamics of trailer sway are complex, but that some sway behaviors can be predicted with relatively simple models.

One thing I'm curious about - where is the dissipative force coming from in the Reese twin cam hitches? It seems as if those bars act more as springs to generate a force proportional to hitch angle than as a traditional damper.

- Bart

[SARGE/AF]

>>hampstead=This is why larger tanks (water, fuel, etc.) often have baffles.<<

Baffles do not stop the water from moving,, it just divides the large mass it into a smaller moving masses. Still creates the same problem but just minimize others such as water slide/Tip.

Sarge