Trailer weight distribution demonstration

Charlie M. (UH & 002 owner/pilot) wrote on 10/5/2016 7:59 AM:
I've wondered if adding a small (1/4" - 3/8") anti sway bar to the
trailer axle would help in most situations. Granted, proper weight is
best, but the anti sway bar may widen the margin. Thoughts?

It's unlikely it will change the dynamics of a single axle trailer.
Ante-sway bars are used on cars and similar to change the roll stiffness
about each axle: generally, an anti-sway bar on the front axle increases
"understeer" and makes the vehicle more stable. A rear bar does the
opposite.

The place to change anti-sway bars is on the tow vehicle. I suspect a
bigger front bar would increase the towing stability, but I think it's
better to get the trailer balance and tire pressures right (ditto for
the tow vehicles tire pressures).

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

On Monday, October 10, 2016 at 9:53:59 PM UTC-7, Eric Greenwell wrote:
Charlie M. (UH & 002 owner/pilot) wrote on 10/5/2016 7:59 AM:
I've wondered if adding a small (1/4" - 3/8") anti sway bar to the
trailer axle would help in most situations. Granted, proper weight is
best, but the anti sway bar may widen the margin. Thoughts?

It's unlikely it will change the dynamics of a single axle trailer.
Ante-sway bars are used on cars and similar to change the roll stiffness
about each axle: generally, an anti-sway bar on the front axle increases
"understeer" and makes the vehicle more stable. A rear bar does the
opposite.

The place to change anti-sway bars is on the tow vehicle. I suspect a
bigger front bar would increase the towing stability, but I think it's
better to get the trailer balance and tire pressures right (ditto for
the tow vehicles tire pressures).

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf

The most stable trailer configuration is a semi where about half the trailer weight is on the tongue. This is not possible for autos which can't support that kind of tongue weight. Even fifth wheels don't put the trailer wheels in that position, and they are accepted to be the most stable trailer configuration.

I have come to realize that there are two moment of inertia of interest; one referenced to the trailer axle and the other referenced to the hitch. Why is MOI important? The answer is if you have an oscillating body it will be harder to stop the larger the MOI. This is why engines have flywheels. If you want to minimize axle MOI you would put as much weight as possible near the axle, which may decrease tongue weight. If you want to minimize hitch MOI you move weight forward, which increases axle MOI. Clearly there is something contradictory about these two MOIs. All trailer towing guides I have seen emphasize maintaining a tongue weight that is 7 to 10% of the total trailer weight. Remember that MOI is calculated as the sum of the weight times the radius SQUARED, so any weight is a long distance from the reference point has a major influence on MOI. If the trailer's tires are maintaining traction with the road the axle MOI is of interest, but if the tires loose traction then the hitch MOI dominates. For certain, putting weight at the rear of the trailer aggravates both MOIs, but increases the hitch MOI four times as much as the axle MOI.

The moral of the story is to manage the hitch weight properly. Merely adding weight to the front of the trailer is not the solution: you should adjust the axle position to get the proper tongue weight. I have done this on one trailer and experimented with trailer transient response as a function of tongue weight. More tongue weight was better.

Tom

Not adding anything to the conversation, but I had purchased a Nimbus 4 that had a Pfister (spelling?) tube trailer. The tongue weight was so heavy it could only be moved by a jack. Soon after getting the bird I purchased a double axle Cobra trailer for the glider and sold the other trailer. The new cobra had a tongue weight much less than the former trailer and could be moved by hand and towed marvelously. Of course back then I was towing with a 2500 chevy Suburban and I had to put a post it on the dash to remind me that I was towing a trailer. While not an expert in any field of this particular discussion, it seems tow vehicle has much to do with the stability as the trailer. My ASw-24 towed towed great behind my little four banger Toyota pick up and horrible behind my next car a Jeep Grand Cherokee. The Suburban was my favorite tow vehicle but I had to keep reminding myself of the trailer. I am currently towing an ASG-29E with a ML 350 diesel and it tows great, but I do have a double exile trailer.

On Friday, October 14, 2016 at 7:24:24 AM UTC-7, Jonathan St. Cloud wrote:
Not adding anything to the conversation, but I had purchased a Nimbus 4 that had a Pfister (spelling?) tube trailer. The tongue weight was so heavy it could only be moved by a jack. Soon after getting the bird I purchased a double axle Cobra trailer for the glider and sold the other trailer. The new cobra had a tongue weight much less than the former trailer and could be moved by hand and towed marvelously. Of course back then I was towing with a 2500 chevy Suburban and I had to put a post it on the dash to remind me that I was towing a trailer. While not an expert in any field of this particular discussion, it seems tow vehicle has much to do with the stability as the trailer. My ASw-24 towed towed great behind my little four banger Toyota pick up and horrible behind my next car a Jeep Grand Cherokee. The Suburban was my favorite tow vehicle but I had to keep reminding myself of the trailer. I am currently towing an ASG-29E with a ML 350 diesel and it tows great, but I do have a double exile trailer.

The Jeep Grand Cherokee has a bad reputation as a tow vehicle. I personally saw one (attempting to) towing a small travel trailer. It was not stable and I witnessed severe swaying at a relatively slow speed (50 mph). The driver would slow down when it went unstable, and then creep back up to the speed that it would go unstable again. It was disturbing to watch - the driver had his family in the car and they were all at risk. I think the problem was the short wheel base in combination with the suspension and the tires. If they are too soft there isn't sufficient damping to stop swaying. This is further aggravated by the length of glider trailers. Yet they are rated to tow pretty hefty trailers. The moral of the story is just because the drive train can handle the trailer weight doesn't mean that it will be stable at highway speeds.

Tom

On Saturday, October 15, 2016 at 11:05:40 PM UTC-7, 2G wrote:
On Friday, October 14, 2016 at 7:24:24 AM UTC-7, Jonathan St. Cloud wrote:
Not adding anything to the conversation, but I had purchased a Nimbus 4 that had a Pfister (spelling?) tube trailer. The tongue weight was so heavy it could only be moved by a jack. Soon after getting the bird I purchased a double axle Cobra trailer for the glider and sold the other trailer. The new cobra had a tongue weight much less than the former trailer and could be moved by hand and towed marvelously. Of course back then I was towing with a 2500 chevy Suburban and I had to put a post it on the dash to remind me that I was towing a trailer. While not an expert in any field of this particular discussion, it seems tow vehicle has much to do with the stability as the trailer. My ASw-24 towed towed great behind my little four banger Toyota pick up and horrible behind my next car a Jeep Grand Cherokee. The Suburban was my favorite tow vehicle but I had to keep reminding myself of the trailer. I am currently towing an ASG-29E with a ML 350 diesel and it tows great, but I do have a double exile trailer.

The Jeep Grand Cherokee has a bad reputation as a tow vehicle. I personally saw one (attempting to) towing a small travel trailer. It was not stable and I witnessed severe swaying at a relatively slow speed (50 mph). The driver would slow down when it went unstable, and then creep back up to the speed that it would go unstable again. It was disturbing to watch - the driver had his family in the car and they were all at risk. I think the problem was the short wheel base in combination with the suspension and the tires. If they are too soft there isn't sufficient damping to stop swaying. This is further aggravated by the length of glider trailers. Yet they are rated to tow pretty hefty trailers. The moral of the story is just because the drive train can handle the trailer weight doesn't mean that it will be stable at highway speeds.

Tom

The older Jeep Cherokee was the same, especially when low on fuel. Install better shocks and it's fine.
Jim

Higher mileage Jeeps are also know for the "Jeep death shake/weave" on their own, even without a trailer. Not a good choice unless worn suspension bits are replaced.
Yes, we owned a 1998 Cherokee Sport for a couple years, lots of bottom bits were replaced.
High CG, tall tires, worn bits, shortish wheel base for its height.

A good tow vehicle should be sorta heavy, long, low (think 60's & 70's US station wagons). Yes, other vehicles can tow (I crewed, about 1979, driving a VW Beetle towing a plywood ASW-15 trailer, it had a hard time doing 55MPH on flat ground.....empty!), but some vehicles have an easier time with ANY trailer.

Is there much point in comparing worn out cars? In my case the boxy '87 Cherokee was bought new, and its first road trip was a 4-day drive to pick up an LS4.
Took a lot of messing around with the trailer and car to find the real fix.
Jim

On Sunday, October 16, 2016 at 9:33:32 AM UTC-5, Charlie M. (UH & 002 owner/pilot) wrote:
Higher mileage Jeeps are also know for the "Jeep death shake/weave" on their own, even without a trailer. Not a good choice unless worn suspension bits are replaced.
Yes, we owned a 1998 Cherokee Sport for a couple years, lots of bottom bits were replaced.
High CG, tall tires, worn bits, shortish wheel base for its height.

You can tow with a Jeep Cherokee, but you have to have everything setup correctly: upmarket tires at max PSI, air shocks on rear axle, proper tongue weight, trailer tires at correct pressure and type. With that, my old 1997 Cherokee Sport with 230K miles tows fine up to 70 mph (15m Cobra with trailer tires). But it took a while to sort it out! (and the brakes are marginal going down long hills...)

But a longbed pickup - or an RV? Can't even tell there is a trailer behind....

Now when you have to pull that trailer out of the middle of a huge disced field in the middle of nowhere at 2 AM - that 4WD Cherokee is nice to have around, warts and all. Which is why it's still in my garage.

Horses for courses, is the saying I believe.

Kirk
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