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.