bmario,
When you have flown the Wing Dragon Sportster or the 4 for a bit and you get a critical eye you'll notice the wings flexing a good bit and there are a couple of good ways to cover this problem. The easy wing fix will be first here.
Purchase a roll of 2 inch, fiber reinforced packing Tape and to make the wing some what stiffer, run a piece the length of each wing placing the center of the LE in the center of the wing. In addition to a small strengthening factor, this adds damage resistance when stricking small obstacles on take off and landing. Then run a strip on both top and bottom, as close to the thickest part of the wing, from tip to root. You will now have spar strength to prevent most wing failures due to Snap Rolls, Split S's as well as inside and outside loops.
Now use a cheeper but lighter 2 inch clear packing tape to protect your wing tips from Runway Rash. Next protect the rear control surfaces by running a half inch to three quarter reinforced tape from tip to tip on the Horizontal Stabelizer and a strip along the leading edge will prevent dings. A strip of clear on thde bottom outside tips of the Stabelizer is a good idea for this area also.
I will be doing this to mine until I can pull all of my material together for a more lasting and stronger fix. Before you fly thye modified aircraft go to the high grass again and make sure it's still in trim. The most balast you will need is a quarter ounce of Play Dough inside the nose, pressed into the tip.
My permanent fix will involve thin by thin Carbon Fiber strips, One in the leading edge and one contineous strip from the Root to the Tip of each wing on the top and the bottom of each wing. I will also, likely, epoxy the two wings together. Researching, I have found that there is a Foam Friendly CA Glue that I will use to hold the Carbon Fiber Strips in place. The Carbon Fiber Strips can be found on line for less than $1.50 each. After they are glued in place and cured, sand the ends to fit the wing tip shape.
Again, happy landings.<br type="_moz" />