Thanks for posting this Doug in BC. In this case a you tube video is worth a thousand words.
I see that his trailer axle
can also be adjusted forward and back on the model. It looks like it is set at about 60/40 with 60% of the tongue or frame length in front of the axle
and 40% behind.
Lets do some mental exercises:
What if the trailer axle
were slid back to 80/20 and all three of the weights were put on the back? It would be the exact same total trailer weight
but how would that affect the tongue weight? Would it still fishtail? What about at 90/10? What about if you slide it forward to 50/50 and do nothing but adjust weights? Which would be the more stable?
While we are at it lets construct a model tow car with a wheel base (distance from the front steering axle to the rear axle) of say 10 inches. Add a draw bar (hitch), with a little ball or hitch pin on the end of it, that can be moved in and out (closer or farther from the rear car axle). Set the trailer weight and tongue length at 60/40 like the you tube guy had it and then try different draw bar distances from the tow car axle, say 10% of the tow vehicle wheel base up to say 50% of the tow vehicle wheel base. What effect would those changes have on trailer stability?
Then if you want to do a really in depth study you can build your model tow vehicle with an adjustable length wheel base and of course adjustable weights front, rear and in the middle. Then you can try all of the length ratios and weight combinations of both the tow vehicle and trailer.
When you complete that course of study you will know more about towing stability dynamics than 99% of trailer manufacturers.