RE: How to construct and tow a banner ??
OK, it's pretty easy.
First, you need a length of banner material....nylon, cotton or whatever. A .40-sized model will easily tow a banner that is about 8 feet long x 1 foot high...rough guide. I've towed bits of old bed-sheet with messages daubed on quite roughly. Household paint is quick and cheap. But, your first experiments don't require a slogan, I guess.
At the front of the banner, you affix a stick, onto which your towing bridle is attached. The stick will, ideally, sit in a pocket which you have sewn into the front of the banner. The stick will ride vertically if you fasten a weight to its base; a couple of ounces will be OK. The towing bridle is fixed to the extremes of the stick. (This is really tricky to describe without pictures.)
So, to labour the point. A single tow-line, perhaps 15 m in length, is fixed to the model's tail. A couple of feet from the banner, the tow-line is bifurcated. One leg is fastened to the top of the stick and one leg to the base of the stick.
The tail of the banner will flap about quite madly unless you can tame it. A few cuts, longitudinally, should help. It will then resemble a kite's tail, except multipally. Or, you can fasten a length of nylon mesh to the tail of the banner...haven't tried this, but I believe that it works.
You can tow from the tail of the model without any problems, but it would be wise to fit a release mechanism....but not vital, as you can readily land with the banner attached; and plenty of power on!
For take-off, lay out the banner and tow line so that they are in front (and to one side) of the model on the runway. In this way, as the model rolls along the runway, the banner and line will gradually "unfurl".....the load will be taken up progressively.
Hope this makes sense to you.