I was encouraged by Spindatt's yoobtube channel on this concern: Note that he was using a QR block in a very high position (strapped to an ordinary rear rack) and, although he said the bike "wanted" to fall over in turns, it never fell and righted itself as it straightened out, post turn.

So, with apologies for the delay, I tested the towing part of my trailer rig and it was a resounding success. Trip was about a mile with normal bumps (road to driveway transitions) and regular intersection turns (as well as unintentional sharper turns when I geared too low and had to crab the bike to stay straight). Not once did the bike flop over. So I'm very happy :thumb:
https://cimg4.ibsrv.net/gimg/bikefor...1d8fda5323.jpg

Finally made a full trip this Saturday and was quite challenging, but in unexpected ways. On the positive side, the Delta QR block (towed single bike frame with just a wheel in back) performed flawlessly for 25 miles to the co op. The BIG problem came in that the wheel QR loosened itself twice during the trip. First time was about half way in the trip and had the trailing bike rocking significantly side to side. A nice rider "gorillaed" the rear wheel QR and everything seemed fine. But the tightening only made it about 10 more miles. Had to tighten again. Was close to the co op so made it without incidence. At no time, thankfully, did the trailing bike threaten to dismount.

So, the mystery that I hope any of you physics people can solve: Why did the tightened, and then strongly tightened, QR work its way loose? Again, this was just an mtb frame with a properly fitting (indeed the wheel I'd been riding on it as a full bike for 100's of miles) wheel and ride tightened QR. A customer at the co op (engineering student) opined that it may be because there was NO weight on the bike and all the bouncing force was concentrated to loosen the QR. Just doesn't seem right, but what do I know? Hopefully someone with experience and knowledge can chime in.

My take away, for now: attach safety lines to any towed bike AND check that it is at least tracking true without wobbles.

As for turns: all ordinary turning was fine. Once in the co op parking lot I intentionally did the sharpest turn (manually) with the trailer and the trailing bike did, eventually, fall over on its side. But, for the whole 25 miles of shake, rattle and roll, the trailing bike tracked upright.

Here's my home-made trailer which I finished just last month. It has 5½ cubic feet of internal space, and more stuff could be strapped on top if necessary, like on a roof rack of a car. (Or, you can just remove the top in a jiffy.) It has 10" solid-rubber tires, and has springs to avoid damage from hitting bumps hard. It's designed to be aerodynamic. The bottom is more or less waterproof, so if I had to go through several inches of water, it'd float like a boat. Although the wheels and suspension parts would get submerged, the insides should stay dry.

https://cimg4.ibsrv.net/gimg/bikefor...9493fcf676.jpg
You can see lots more pictures and description on this page of my website: Wilson Mines Co., road-bike trailer

I'm new to the forum and this is the first time I'm inlining a picture. I hope it shows up correctly.

Wow, it's a boat and a trailer! :D

Awesome job!