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Old 09-07-2019, 06:35 PM   #21
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Lots of good information from David and Ephraim. For instance when the mass of the trailer tongue gets added to the ball the COG of the TV does change.
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Old 09-07-2019, 06:51 PM   #22
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These diagrams, which I borrowed from another forum, help explain the WDH.





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Old 09-07-2019, 08:18 PM   #23
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David, this one paragraph from the study I linked to is key in answering your questions about TW. B2 represents the distance of the trailer COG from the trailer axle centerline. The final two sentences sums it up in saying there is an optimal trailer TW for a towing combination that minimizes static instability and yet still keeps dynamic stability high enough for a required speed. For dynamic stability 10-15% has been determined to be the range. You will find that most studies will ignore the WDH. This is because PE’s know that stability should be achieved by matching the TV and trailer characteristics. From a static instability standpoint adding any amount of WD reduces static instability so it’s use should be minimized. The WDH sway control should not be relied upon to achieve sway/dynamic stability. I can here all you PP/Hensley owners screaming foul and yes it’s a slightly different animal.
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Old 09-07-2019, 09:06 PM   #24
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... I can here all you PP/Hensley owners screaming foul and yes it’s a slightly different animal.
That didn't take long to make it into the realm of personal attacks.
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Old 09-07-2019, 09:12 PM   #25
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That didn't take long to make it into the realm of personal attacks.
There is no personal attacks in that statement.
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Old 09-07-2019, 09:31 PM   #26
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There is no personal attacks in that statement.


Yes there are.
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Old 09-08-2019, 12:07 AM   #27
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I don’t have a technical reference paper to point you to, but I can make a some observations.
The TW required for stability is clearly a function of centre of gravity. A low C of G means that stability can be achieved with a low tongue weight. Boats tow well at 6 or 7%. Airstreams seem very happy at 11%. Tall conventional travel trailers with big slides seem to need 15%. Big 5th wheels seem to have pin weights in the 20% range.
European caravans have tongue weights in the 5 or 6% range, which explains why they have towing speed limits of 80 to 100 km/h (50 to 62 mph).
I am wondering if travel trailer manufacturers employ engineers to make these determinations, or if it’s simply a matter of figuring out what works acceptably well.
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Old 09-08-2019, 12:14 AM   #28
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David, this one paragraph from the study I linked to is key in answering your questions about TW. B2 represents the distance of the trailer COG from the trailer axle centerline. The final two sentences sums it up in saying there is an optimal trailer TW for a towing combination that minimizes static instability and yet still keeps dynamic stability high enough for a required speed. For dynamic stability 10-15% has been determined to be the range. You will find that most studies will ignore the WDH. This is because PE’s know that stability should be achieved by matching the TV and trailer characteristics. From a static instability standpoint adding any amount of WD reduces static instability so its use should be minimized. The WDH sway control should not be relied upon to achieve sway/dynamic stability. I can hear all you PP/Hensley owners screaming foul and yes it’s a slightly different animal.
The Delphi paper, from 2008, was about verifying their computer simulation and not validating tongue weight. Their quote was " general towing guidelines that the tongue weight should be ~ 10 – 15% of the total trailer weight. " They tested three bizarre non-WDH configurations with the goal of trying to simulate instability.

The Hensley/ProPride hitches, and I have one, demonstrate that the stability problem is from lateral forces on the hitch ball hanging ~5.5ft behind the rear axle. Whether 5th wheel, gooseneck, or 4-bar linkage tag along, eliminating those forces fix the stability problem. Is anyone really able to have an Airstream and not also get a $2500 hitch? Owners on other forums have said the only time they see a Hensley/ProPride is on Airstreams.

If you are at 10% uncoupled with a WDH hitch, you are probably at 7.5% in reality.

Moving the CG forward in most cases probably does reduce the pendulum effect. That is not saying 10% is good, it is saying anything to fix that problem helps.

I'm wondering why there aren't any full-trailers (with the full weight on axles front and rear), every trailer is a semi (where the front weight is on the towing vehicle). It would seem a logical solution to the payload issue.

Note that GVWR and to a less extent GAWR are also measurements that cause havoc in configuring 1/2 ton and lower towing configurations because of their limitations that have no standards.

For example, rear axles of 1/2 ton pickups and SUVs typically fall between 3800lb and 4300lb. Is this really just a tire, wheel, and spring issue? Does adding stronger wheels, LT tires, and supplemental air springs raise that to maybe 5000lb or even 5300lb (to the best of my knowledge there are no 5 or 6 lug wheels rated above 2650lb).

Would the combined 9000lb combined GAWRs mean an 8000lb GVWR is reasonable? Note the Suburban 2500 had a GVWR of 8600lb. A 5000lb rear GAWR with an 8000GVWR would make even heavily optioned 1/2 ton pickups able to hit their 17000+lb GCWR (which is measured to the J2807 standard).

Note that the 10+% guideline requires a lot more tension on the WD bars, which couples the trailer to the tow vehicle in the vertical plane. That alone hurts ride and handling reducing the safety margin.

Many travel trailer designs try to keep the heavy stuff near the wheels or forward. However, then there are designs like this. I'm guessing the plumbing and kitchen weigh more than the bed:



Which just brings us full circle. What is the minimum tongue weight and what is the contraining condition?
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Old 09-08-2019, 06:27 AM   #29
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The formulas used in the Delphi study is basic engineering based on the single track model, they are not specific to this one study. The answer has been given to you by myself and others so I will only make the assumption that you don’t understand the concept. I will leave you with a link which describes some basic concepts, even though it’s from down under trailers sway no differently.

https://practicalmotoring.com.au/car...eavy-trailers/
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Old 09-08-2019, 09:28 AM   #30
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I'm wondering why there aren't any full-trailers (with the full weight on axles front and rear), every trailer is a semi (where the front weight is on the towing vehicle). It would seem a logical solution to the payload issue.
Hi

Because they would be a royal pain to turn when backing into a site. Even a 3 axle AS gets into this problem compared to a 2 axle.

Again - tongue weight is a static measure. Stability is a dynamic issue. Any connection between the two is not very tight.

Bob
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Old 09-08-2019, 11:29 AM   #31
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Originally Posted by DavidNJ View Post
The Delphi paper, from 2008, was about verifying their computer simulation and not validating tongue weight. Their quote was " general towing guidelines that the tongue weight should be ~ 10 – 15% of the total trailer weight. " They tested three bizarre non-WDH configurations with the goal of trying to simulate instability.



The Hensley/ProPride hitches, and I have one, demonstrate that the stability problem is from lateral forces on the hitch ball hanging ~5.5ft behind the rear axle. Whether 5th wheel, gooseneck, or 4-bar linkage tag along, eliminating those forces fix the stability problem. Is anyone really able to have an Airstream and not also get a $2500 hitch? Owners on other forums have said the only time they see a Hensley/ProPride is on Airstreams.



If you are at 10% uncoupled with a WDH hitch, you are probably at 7.5% in reality.



Moving the CG forward in most cases probably does reduce the pendulum effect. That is not saying 10% is good, it is saying anything to fix that problem helps.



I'm wondering why there aren't any full-trailers (with the full weight on axles front and rear), every trailer is a semi (where the front weight is on the towing vehicle). It would seem a logical solution to the payload issue.



Note that GVWR and to a less extent GAWR are also measurements that cause havoc in configuring 1/2 ton and lower towing configurations because of their limitations that have no standards.



For example, rear axles of 1/2 ton pickups and SUVs typically fall between 3800lb and 4300lb. Is this really just a tire, wheel, and spring issue? Does adding stronger wheels, LT tires, and supplemental air springs raise that to maybe 5000lb or even 5300lb (to the best of my knowledge there are no 5 or 6 lug wheels rated above 2650lb).



Would the combined 9000lb combined GAWRs mean an 8000lb GVWR is reasonable? Note the Suburban 2500 had a GVWR of 8600lb. A 5000lb rear GAWR with an 8000GVWR would make even heavily optioned 1/2 ton pickups able to hit their 17000+lb GCWR (which is measured to the J2807 standard).



Note that the 10+% guideline requires a lot more tension on the WD bars, which couples the trailer to the tow vehicle in the vertical plane. That alone hurts ride and handling reducing the safety margin.



Many travel trailer designs try to keep the heavy stuff near the wheels or forward. However, then there are designs like this. I'm guessing the plumbing and kitchen weigh more than the bed:







Which just brings us full circle. What is the minimum tongue weight and what is the contraining condition?


I just happen to have actual weights for the trailer in your attachment. Actually an earlier FC23FB, but minimal change as far as weight. The last sentence was my experiment with added rear weight.

Jalan Jalan Weights, lbs
Tongue785
Right Front1260
Left Front1332
Front Axle2592
Right Rear1187
Left Rear1109
Rear Axle2296
Total Trailer5673
% Tongue Weight14%
Equalizer Hitch Assembly91
“Hitch Weight” on Receiver876

Normal Towing Loads
Full Fresh Tank
Empty Waste Tanks
Full Propane Tanks
Digital Automotive Scales (4)

With additional 190 lbs on rear bumper, tongue weight = 655 lbs12%

Good discussion, appreciate the technical analysis.


Safe Travels,
JamuJoe
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Old 09-08-2019, 12:08 PM   #32
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And your statement is why I have very little to do with this forum any more.
Good luck.


Overlander,
Sorry, no offense intended. A risk of ‘social media’. Just trying to go beyond the single sentence ‘rules of thumb’ to deeper analysis.
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Old 09-08-2019, 04:03 PM   #33
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Originally Posted by uncle_bob View Post
Hi

Because they would be a royal pain to turn when backing into a site. Even a 3 axle AS gets into this problem compared to a 2 axle.

Again - tongue weight is a static measure. Stability is a dynamic issue. Any connection between the two is not very tight.

Bob
Is was thinking a steered front wheel like this:



Quote:
Originally Posted by Profxd View Post
The formulas used in the Delphi study is basic engineering based on the single track model, they are not specific to this one study. The answer has been given to you by myself and others so I will only make the assumption that you don’t understand the concept. I will leave you with a link which describes some basic concepts, even though it’s from down under trailers sway no differently.

https://practicalmotoring.com.au/car...eavy-trailers/
Rather than argue over the Delphi report, let's look at the video in the article you posted.



Basically, as I said, it is the polar moment. If it was CG that is what we'd be talking about. Meanwhile, 5th wheel, gooseneck, adn 4-bar linkage mounts don't have a sway problem regardless of CG. They still have an overhang problem, which is worse in a low car hauler.

For some reason my post from yesterday afternoon still hasn't been posted, I'll include it here:

Quote:
Sway is a dynamic situation. Tongue weight (as normally defined) is a static measurement. Basic physics dictates that one is *not* the same as the other. ​

The reason you see ~ 10% tongue weights is a practical one. You don't want the trailer dropping on it's back bumper when unhitched. Practical experience with people loading trailers over the years suggests that 10% is "enough" to keep this from happening. Indeed if you dig into boat trailers you *will* find cases of backwards tip ....​

Axle ratings are not the same as receiver ratings. Moving weight between the axles still puts strain ( = load) on the receiver. It still can / will be damaged if overloaded. The numbers that truck factories guess at when putting on receivers are in no way a guarantee that everything will be fine. You do need to check *all* the numbers. ​

If you want to dig further into the physics of sway, a good place to start is with the higher order moments of inertia and how they are calculated. Control systems theory would be the next step in the study course. Ultimately you will come up with a chart of phase margin (or gain peaking) vs speed vs weight location for a specific rig. ​

Bob
Thanks for the insights. I've thought the 10% may have occurred to have a number too high to cause the tow vehicle rear axle to be unloaded. If that were an issue it would be discussed. It isn't mentioned anywhere.

Do you know the approximate year the WDH was invented and marketed and who was the original company?

Polar moment is a bigger factor than MOI. Take the ball which can only transmit axial force. towing a 25ft box trailer, 10ft behind the centerline of the axle. A 5ft tongue gives a total length of 30ft.

A 100lb lateral force at the front of the box creates 500 lb-ft moment around the ball which is resisted by a 25lb lateral force on the trailer axle (and 75lb on the ball). That same lateral force on the rear edge of the trailer creates a 3000 lb-ft moment that is resisted by 150lb lateral force on the trailer axle (and 50 lb force on the ball in the opposite direction).

The typical towing ball is 5.5ft from the tow vehicle axle, more on some. those forces create 410 lb-ft and 275 lb-ft moments around the tow vehicle rear axle. With a 12ft wheelbase (typical of a 1/2ton short-bed pickup) that would be a 34lb and 23lb lateral force on the front tires

Those forces are a function of the placement of the trailer axle rather than the placement of static weight although, like a pendulum, static weight's polar moment counts. Note that on an 18-wheel tractor-trailer, the wheels are placed at the extreme rear of the trailer. On 5th-wheel trailers for pickups, that is limited by the payload and rear axle capacity of the pickup.

A Hensley or Propride hitch would have moved the virtual pivot point to maybe 16" behind the tow vehicle's rear axle. That would have made the moments about the rear axle 8 lb-ft and 6 lb-ft.

Obviously, is sway is a problem the owner should have a Hensley or ProPride hitch. To tow a $50k antique car in a $20k aluminum trailer, or on this forum a $50+k RV on an $800 WDH when $2800 4-bar linkage WDH hitch behind a $70k tow vehicle would solve the problem is probably not a sound risk analysis.

Which leads to the other problem. That $70k tow vehicle has a 10klb or 12lk pound receiver from the factory, and the advertisements talk about 1800lb-2000lb payloads, but the reality is different. The payload numbers are for stripped work trucks with heavy-duty springs that would yield an unacceptable unloaded ride. Loaded with options at the "Limited" level, these vehicles often have door stickers with 1100lb-1300lb payloads...or less. That makes most towing problematic with 4 people and some luggage in the tow vehicle.

If a lower disconnected tongue weight and weight transfer from the WDH are put in play, the net additional load for a 10k trailer could be 500lb, for an 8k trailer 400lb...or even slightly less.

Further, less tension in the WD bars allows more movement between the tow vehicle and the trailer which should result in a better ride and better handling.

The $64k question is: what is the real limiting factor on minimum tongue weight when towing heavy.

https://youtu.be/6mW_gzdh6to[/QUOTE]

And before I wrap up...this is a cute device from Australia. Can't find it in the US. A small box with accelerometers (no gyro?) that detects 'sway' and applies the trailer brakes.
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Old 09-08-2019, 04:13 PM   #34
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Originally Posted by uncle_bob View Post
Hi

Because they would be a royal pain to turn when backing into a site. Even a 3 axle AS gets into this problem compared to a 2 axle.

Again - tongue weight is a static measure. Stability is a dynamic issue. Any connection between the two is not very tight.

Bob
Is was thinking a steered front wheel like this:



Quote:
Originally Posted by Profxd View Post
The formulas used in the Delphi study is basic engineering based on the single track model, they are not specific to this one study. The answer has been given to you by myself and others so I will only make the assumption that you don’t understand the concept. I will leave you with a link which describes some basic concepts, even though it’s from down under trailers sway no differently.

https://practicalmotoring.com.au/car...eavy-trailers/
Rather than argue over the Delphi report, let's look at the video in the article you posted.



Basically, as I said, it is the polar moment. If it was CG that is what we'd be talking about. Meanwhile, 5th wheel, gooseneck, adn 4-bar linkage mounts don't have a sway problem regardless of CG. They still have an overhang problem, which is worse in a low car hauler.

For some reason my post from yesterday afternoon still hasn't been posted, I'll include it here:

Quote:
Sway is a dynamic situation. Tongue weight (as normally defined) is a static measurement. Basic physics dictates that one is *not* the same as the other. ​

The reason you see ~ 10% tongue weights is a practical one. You don't want the trailer dropping on it's back bumper when unhitched. Practical experience with people loading trailers over the years suggests that 10% is "enough" to keep this from happening. Indeed if you dig into boat trailers you *will* find cases of backwards tip ....​

Axle ratings are not the same as receiver ratings. Moving weight between the axles still puts strain ( = load) on the receiver. It still can / will be damaged if overloaded. The numbers that truck factories guess at when putting on receivers are in no way a guarantee that everything will be fine. You do need to check *all* the numbers. ​

If you want to dig further into the physics of sway, a good place to start is with the higher order moments of inertia and how they are calculated. Control systems theory would be the next step in the study course. Ultimately you will come up with a chart of phase margin (or gain peaking) vs speed vs weight location for a specific rig. ​

Bob
Thanks for the insights. I've thought the 10% may have occurred to have a number too high to cause the tow vehicle rear axle to be unloaded. If that were an issue it would be discussed. It isn't mentioned anywhere.

Do you know the approximate year the WDH was invented and marketed and who was the original company?

Polar moment is a bigger factor than MOI. Take the ball which can only transmit axial force. towing a 25ft box trailer, 10ft behind the centerline of the axle. A 5ft tongue gives a total length of 30ft.

A 100lb lateral force at the front of the box creates 500 lb-ft moment around the ball which is resisted by a 25lb lateral force on the trailer axle (and 75lb on the ball). That same lateral force on the rear edge of the trailer creates a 3000 lb-ft moment that is resisted by 150lb lateral force on the trailer axle (and 50 lb force on the ball in the opposite direction).

The typical towing ball is 5.5ft from the tow vehicle axle, more on some. those forces create 410 lb-ft and 275 lb-ft moments around the tow vehicle rear axle. With a 12ft wheelbase (typical of a 1/2ton short-bed pickup) that would be a 34lb and 23lb lateral force on the front tires

Those forces are a function of the placement of the trailer axle rather than the placement of static weight although, like a pendulum, static weight's polar moment counts. Note that on an 18-wheel tractor-trailer, the wheels are placed at the extreme rear of the trailer. On 5th-wheel trailers for pickups, that is limited by the payload and rear axle capacity of the pickup.

A Hensley or Propride hitch would have moved the virtual pivot point to maybe 16" behind the tow vehicle's rear axle. That would have made the moments about the rear axle 8 lb-ft and 6 lb-ft.

Obviously, is sway is a problem the owner should have a Hensley or ProPride hitch. To tow a $50k antique car in a $20k aluminum trailer, or on this forum a $50+k RV on an $800 WDH when $2800 4-bar linkage WDH hitch behind a $70k tow vehicle would solve the problem is probably not a sound risk analysis.

Which leads to the other problem. That $70k tow vehicle has a 10klb or 12lk pound receiver from the factory, and the advertisements talk about 1800lb-2000lb payloads, but the reality is different. The payload numbers are for stripped work trucks with heavy-duty springs that would yield an unacceptable unloaded ride. Loaded with options at the "Limited" level, these vehicles often have door stickers with 1100lb-1300lb payloads...or less. That makes most towing problematic with 4 people and some luggage in the tow vehicle.

If a lower disconnected tongue weight and weight transfer from the WDH are put in play, the net additional load for a 10k trailer could be 500lb, for an 8k trailer 400lb...or even slightly less.

Further, less tension in the WD bars allows more movement between the tow vehicle and the trailer which should result in a better ride and better handling.

The $64k question is: what is the real limiting factor on minimum tongue weight when towing heavy.

[/QUOTE]

And before I wrap up...this is a cute device from Australia. Can't find it in the US. A small box with accelerometers (no gyro?) that detects 'sway' and applies the trailer brakes.

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Old 09-08-2019, 05:18 PM   #35
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electronic sway control

You might look at these folk's products. And there is an SOB mfg that sells the electronic sway control as an option. CanAm tested one of the products. Pat

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Old 09-08-2019, 07:21 PM   #36
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There is a paper directly about this

The paper: An experimental investigation of car-trailer high-speed stability

This is from the University of Bath. It is on point but didn't test with a WDH. They looked at tongue weight (they call it nose mass), trailer mass, moment of inertia, tire pressure and axle position. These are the folks who made some of the 'model car on a rolling roadway' videos.

Interestingly, the percentage tongue weight they tested for was -0.8% to 10.5%. They found "an increased nose mass improved the system stability, although the improvement becomes less significant when the nose mass rises above 6–7 percent of the total weight."

Another finding: "when the trailer inertia increases, the damping of the combined car–trailer system decreases dramatically. The inertia effect suggests that, when a driver is loading a caravan, the mass should be placed as close to the centre of gravity as possible in order to minimize the resulting increase in inertia."

Their conclusions:

Quote:
CONCLUSIONS
Very little work has been published on the experimental measurement of high-speed car–trailer stability. In this study, extensive experimental measurements were carried out on a combined car–adjustable-trailer system. By adjusting the trailer settings, the effect of different trailer parameters on the system stability was examined. It was found that the dominant factors affecting stability were the trailer yaw inertia, nose mass (load distribution), and trailer axle position. The tyre pressure also affects the stability, although the effect is less significant. It is interesting to see that the trailer mass alone does not dramatically affect the stability; however, as a heavier trailer normally has a larger yaw inertia, a limit should be placed on the relative car–trailer masses.

A friction stabilizer is shown to be helpful in improving the system stability, although in these tests the stability was not increased hugely. In addition, high-speed towing tests were carried out on cars fitted with an ESP which automatically brakes individual wheels and controls the engine throttle position should the vehicle dynamic response differ from that expected. These tests demonstrated that, if the dynamic response ‘error’ exceeded a preset threshold level, the ESP operated and the highspeed stability was improved by controlling the car yaw oscillation associated with trailer instability.
This begged the question: what is the noseweight standard in the UK? Answer: 5%-to-7%. And they don't seem to be picky. They basically say it is the 5%-to-7% or constrained to the lowest of what the tow vehicle, hitch, or trailer is rated for.

These are two articles and a video:

How to measure and adjust your caravan’s noseweight

Caravan Club Leaflet: Noseweight

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Old 09-09-2019, 04:21 AM   #37
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So I gather from your post that didn’t show up that you believe that % of tongue weight has nothing to do with sway? Sway is caused by polar moments or is it trailer axle position?
Richard H Klein has done a study back in the 70’s on finding the optimal hitch weight. The outcome is that you need to minimize hitch weight yet keep enough TW to maintain sway stability for a given speed as well as minimize the use of WD.
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Old 09-09-2019, 09:28 AM   #38
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Quote:
Originally Posted by DavidNJ View Post
Is was thinking a steered front wheel like this:





Rather than argue over the Delphi report, let's look at the video in the article you posted.



Basically, as I said, it is the polar moment. If it was CG that is what we'd be talking about. Meanwhile, 5th wheel, gooseneck, adn 4-bar linkage mounts don't have a sway problem regardless of CG. They still have an overhang problem, which is worse in a low car hauler.

For some reason my post from yesterday afternoon still hasn't been posted, I'll include it here:



Thanks for the insights. I've thought the 10% may have occurred to have a number too high to cause the tow vehicle rear axle to be unloaded. If that were an issue it would be discussed. It isn't mentioned anywhere.

Do you know the approximate year the WDH was invented and marketed and who was the original company?

Polar moment is a bigger factor than MOI. Take the ball which can only transmit axial force. towing a 25ft box trailer, 10ft behind the centerline of the axle. A 5ft tongue gives a total length of 30ft.

A 100lb lateral force at the front of the box creates 500 lb-ft moment around the ball which is resisted by a 25lb lateral force on the trailer axle (and 75lb on the ball). That same lateral force on the rear edge of the trailer creates a 3000 lb-ft moment that is resisted by 150lb lateral force on the trailer axle (and 50 lb force on the ball in the opposite direction).

The typical towing ball is 5.5ft from the tow vehicle axle, more on some. those forces create 410 lb-ft and 275 lb-ft moments around the tow vehicle rear axle. With a 12ft wheelbase (typical of a 1/2ton short-bed pickup) that would be a 34lb and 23lb lateral force on the front tires

Those forces are a function of the placement of the trailer axle rather than the placement of static weight although, like a pendulum, static weight's polar moment counts. Note that on an 18-wheel tractor-trailer, the wheels are placed at the extreme rear of the trailer. On 5th-wheel trailers for pickups, that is limited by the payload and rear axle capacity of the pickup.

A Hensley or Propride hitch would have moved the virtual pivot point to maybe 16" behind the tow vehicle's rear axle. That would have made the moments about the rear axle 8 lb-ft and 6 lb-ft.

Obviously, is sway is a problem the owner should have a Hensley or ProPride hitch. To tow a $50k antique car in a $20k aluminum trailer, or on this forum a $50+k RV on an $800 WDH when $2800 4-bar linkage WDH hitch behind a $70k tow vehicle would solve the problem is probably not a sound risk analysis.

Which leads to the other problem. That $70k tow vehicle has a 10klb or 12lk pound receiver from the factory, and the advertisements talk about 1800lb-2000lb payloads, but the reality is different. The payload numbers are for stripped work trucks with heavy-duty springs that would yield an unacceptable unloaded ride. Loaded with options at the "Limited" level, these vehicles often have door stickers with 1100lb-1300lb payloads...or less. That makes most towing problematic with 4 people and some luggage in the tow vehicle.

If a lower disconnected tongue weight and weight transfer from the WDH are put in play, the net additional load for a 10k trailer could be 500lb, for an 8k trailer 400lb...or even slightly less.

Further, less tension in the WD bars allows more movement between the tow vehicle and the trailer which should result in a better ride and better handling.

The $64k question is: what is the real limiting factor on minimum tongue weight when towing heavy.

And before I wrap up...this is a cute device from Australia. Can't find it in the US. A small box with accelerometers (no gyro?) that detects 'sway' and applies the trailer brakes.

[/QUOTE]

Hi

If you take a look at the track the tires need to clear in your "steered axle" approach, they pretty much have to pass *under* the trailer. That gets you into something that looks a lot more like a 5th wheel than a conventional trailer. There also is the issue of the rear of the TV going under the trailer unless you lengthen the tongue. Greater OAL is generally not a good thing.

======

The whole issue of stability is a three dimensional problem. Front / back / top /bottom / left / right all impact how stable things are going to be. If you are free to move mass in all directions, you can very much come up with stability issues regardless of a specific tongue weight .

A 30' Classic is one example of that. Put water in the tanks and it's stable. Run it dry, much less so. Tongue weight does not change since the tanks are over the trailer axle. Buy one and play a bit if you *really* are interested.

Bob
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Old 09-09-2019, 07:50 PM   #39
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Quote:
Originally Posted by uncle_bob View Post
And before I wrap up...this is a cute device from Australia. Can't find it in the US. A small box with accelerometers (no gyro?) that detects 'sway' and applies the trailer brakes.

Hi

If you take a look at the track the tires need to clear in your "steered axle" approach, they pretty much have to pass *under* the trailer. That gets you into something that looks a lot more like a 5th wheel than a conventional trailer. There also is the issue of the rear of the TV going under the trailer unless you lengthen the tongue. Greater OAL is generally not a good thing.

======

The whole issue of stability is a three dimensional problem. Front / back / top /bottom / left / right all impact how stable things are going to be. If you are free to move mass in all directions, you can very much come up with stability issues regardless of a specific tongue weight .

A 30' Classic is one example of that. Put water in the tanks and it's stable. Run it dry, much less so. Tongue weight does not change since the tanks are over the trailer axle. Buy one and play a bit if you *really* are interested.

Bob[/QUOTE]

Engineers refer what you call three dimensional as degrees of freedom. The basic single track model shown in the study link has 4 degrees of freedom which accounts for most of the parameters needed to determine stability. You can take it out to 24 degrees of freedom if you like to be very precise.

So how can you get a trailer to behave with low tongue weight less than 10%?

#1 best thing you could do is extend the effective tongue length. Making the front A frame longer by 2-3 ft. will increasing stability. The longer the distance from the hitch point to the trailer axle center the better the stability. Moving the axles rearward would increase TW so this one maybe impractical for many trailers.

#2 is about the TV and the distance from the hitch point to the TV center of gravity. The further away the TV COG is from the hitch point increases stability. This is why going from a TV that weighs 5500 lbs to one that weighs 7500 lbs make a difference. Wheelbase definitely helps but it’s the distribution and amount of mass of the TV that’s important. Adding TW(mass) to the TV moves it’s COG rearward. Also the increased TV mass will increase the tire cornering stiffness(grip) which adds to stability. This one is a win win.

#3 is reduce the yaw inertia of the trailer. The more weight that’s centralized around the axles and COG the lower the yaw inertia, stability increases.
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Old 09-09-2019, 08:22 PM   #40
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There doesn’t appear to be an acknowledgement here that 10% isn’t magic, it is simply a rule of thumb for typical North American trailer designs, with their typical moments of inertia. Euro trailers typically have masses such as appliances and tanks very close to the trailer axle centreline, because they are designed for 5% tongue weight.

Boat trailers similarly work well with 5%, because the mass of the engine(s) is very close to the axle centreline, in addition to the relatively long trailer axle to hitch distance.
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