trailer sway mitigation TSM

Matt Herron Jr. wrote on 12/17/2019 8:06 AM:
On Monday, December 16, 2019 at 4:43:23 PM UTC-8, JS wrote:
Good shocks seemed to have the biggest effect in my experience.
Look out when moving trailer weight forward... Never exceed the maximum tongue weight!
Jim

Also tighten up the hitch in the receiver with one of these: they take out the slop that can add to sway, and quiet down the rig

That item raised the safe towing speed about 5 mph on my Sienna minivan; raising
the van tire pressure to the value on the door sticker improved it another 3 mph.
Raising the trailer tire pressure to 10 psi over the pressure required for the
load improved it further, but I don't recall the amount it changed.

--
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

On Monday, December 16, 2019 at 6:41:28 PM UTC-5, Bob Kuykendall wrote:
...These are the things I have done to mitigate trailer sway

Reminds me of when I was a wee glider pilot at MIT Soaring Association.
Instructor: Once, we had a big problem with a trailer swaying.
Dave: So, what did you do?
Instructor: Obviously, we adjusted the center of precussion and moved the axle back.
Dave: So, what happened?
Instructor: It didn't sway anymore, but then the tongue broke off.....

Yup, such was my education.
Couldn't make this stuff up if you tried...

On Monday, December 16, 2019 at 5:44:28 PM UTC-8, Dave Nadler wrote:
On Monday, December 16, 2019 at 6:41:28 PM UTC-5, Bob Kuykendall wrote:
...These are the things I have done to mitigate trailer sway

Reminds me of when I was a wee glider pilot at MIT Soaring Association.
Instructor: Once, we had a big problem with a trailer swaying.
Dave: So, what did you do?
Instructor: Obviously, we adjusted the center of precussion and moved the axle back.
Dave: So, what happened?
Instructor: It didn't sway anymore, but then the tongue broke off.....

Yup, such was my education.
Couldn't make this stuff up if you tried...

Sounds like a group of scientists, not engineers.

On Monday, December 16, 2019 at 5:41:28 PM UTC-6, Bob Kuykendall wrote:
I've rigged, fitted, towed, and modified a bunch of trailers. These are the things I have done to mitigate trailer sway (in order of effectiveness):

1. Longer trailer tongue. Longer is always better at reducing sway. Unfortunately it also increases trailer overall length, tripping hazard, etc.

2. Mass and CG management for trailer. Move weight out of the tail, but maintain modest tongue weight (~5-10% of trailer mass). A single-seater trailer shouldn't weigh more than about 900 lbs.

3. Stiffer tow car rear springs and shocks.

4. Stiffer tow car rear tires.

5. Stiffer trailer tires.

Things that are generally more trouble than they're worth:

* Supplemental sway dampers--They're a pain in the ass bandaid for other trailer issues, and you can't depend on random crews to rig them properly.

* Tongue weight over 10% of trailer mass--Deteriorates car handling more than it improves trailer handling, and makes your trailer a pain to rig and tow.

* Dual trailer axles--Maybe OK for a two-seater, but generally makes your trailer a pain to handle without a tow car.

--Bob K.

I would add one more thing high at the top of the list (provided someone is considering the right type of a car for towing): short distance between the rear axle and the trailer hitch, meaning a car with a short back. My Mazda CX-5 is excellent in that respect, never had any issues with swaying, and I have towed my Ventus across the US more than once, including 75 mph through Texas.

On Monday, December 16, 2019 at 2:03:02 PM UTC-6, princiar wrote:
Anyone has experience towing a trailer with a car with the trailer sway mitigation installed?

Reduce the polar moment of inertia of the trailer - remove mass from the back end of the trailer. Here is a really effective video to describe the problem and its solution:
https://www.youtube.com/watch?v=6mW_gzdh6to
You would be surprised how small additions of mass near the back of the trailer can cause big problems.

My question is related to this, see https://www.youtube.com/watch?v=1sbIsIDtxfI , I tow a doble seeter with single axle and is quite unstable even with all possible weight forward.

Longer wheelbase on the towing vehicle with a robust suspension.

On Tuesday, December 17, 2019 at 5:51:09 AM UTC-8, Glidergeek wrote:
Longer wheelbase on the towing vehicle with a robust suspension.

Perhaps an even more important metric is the ratio between the wheelbase and the distance from the rear axle to the hitch ball. Long wheelbase with the hitch close to the axle is best. Short wheelbase with long distance between the rear axle and hitch gives the trailer more leverage over the car, and the car less leverage against the ground to resist lateral disruption.

--Bob K.

On Monday, December 16, 2019 at 2:03:02 PM UTC-6, princiar wrote:
Anyone has experience towing a trailer with a car with the trailer sway mitigation installed?

I posted a link to a short video before, here are better ones from a Prof at the University of Bath:
https://www.youtube.com/watch?v=PFzrWHTG5e8
https://www.youtube.com/watch?v=qEWtBV9I0U4
There are other videos from the University, that I cannot find quickly now, that show this demonstration rig being used where overall weight of the load is maintained, and even tongue weight. All these videos show that placing load aft is the problem (increased yaw inertia, increased polar moment of inertia, ...).

When towing a homemade Ka-6 trailer with a Ford Explorer along I-40 into Santa Rosa about 20 years ago, I had my first experience with trailer instability. The rig was towing fine along at highway speeds on the level, but as I started down the long curving grade into town, the rig started to speed up slightly. At the same time, I got a gust off a semi I was passing and the trailer started to oscillate. I dared not hit the brakes too hard, but I was going down a grade and the rig was trying to pick up speed. The road also had a mild turn to the right, just to aggravate the problem. I firmly held the steering wheel to avoid amplifying the motion and got the rig to slow just enough to be stable again. By this time, the semi and everyone else who had been near me, were over a quarter of a mile behind me. They had all slowed hard to avoid my issue. Before this trip, I screwed down a lightweight plastic tub in the back of the trailer and put two sleeping bags inside for our kids. I did experiments on level ground and found that the weight of those two sleeping bags placed at the back of the trailer would lower the speed for stability by about 10 miles per hour. We found another place for the sleeping bags for the trip home.

I also have a large, eastern-European, box trailer that I haul a Ka-2b in and use for other glider projects, typically with a Ford E-150 van. After loading up a project near Manning, South Carolina, I realized that the rig was neutrally stable at a speed of about 55 mph. Before getting on the interstate highway, I pulled a box of various broken wood pieces (ribs, etc) out of the back of the trailer and put it in my van. This box was not heavy, just large, which is why I put it in the back of the trailer in the first place. This small change allowed me to tow on the interstate comfortably up to about 65 mph with neutral stability being above 70 mph. I accepted that limitation and observed it for the trip back to Kansas.

With my usual Ka-2b glider situated in the large trailer, I have never reached a neutral stability speed. If there had been a problem, I would have moved the axle aft on the trailer to get stability margin for highway speed.

If your trailer has too much weight aft, it will limit the speed you can drive. Tow vehicle size and tire pressures are all factors, but the primary excitation comes from the stability of the trailer itself. If there too much load aft on the trailer, nothing else will prevent the problem.

I check every trailer I tow by increasing speed by steps and checking for stability with a small steering wheel jerk. I don't want any surprises.

On Monday, December 16, 2019 at 12:03:02 PM UTC-8, princiar wrote:
Anyone has experience towing a trailer with a car with the trailer sway mitigation installed?

I used to tow a DG 800 with a single axle trailer with a 4 Runner and found it got to be quite a adventure. Any rapid turning would end up with a sway side to side. I now tow with a Range Rover with 20" wheels with low profile tires. The difference is night and day. IT was easy to understand the the major difference is the tires. The 4 Runner had a high profile tire that flexed if you pushed side to side on the rear of the car. The low profile tires have virtually no sidewall flex. The suspension in the 4 runner was solid with great sway bars, they however could not over come the flexing in the tire sidewalls. In the Rover I can easily go any speed I desire with zero sway and can change lanes at will. Push your car sideways at the rear and observe what you see. Any motion will reveal why you have sway. I have seen many work arounds with friction tuning to dampen sway, but none work better than addressing the root cause.