Hi Larry,
Shades of the Richland NATS, & boy that was fun! This IS indeed an engineering challenge to design a decent flying model designed to survive crashes into concrete!
Due to a new home project, I can only offer an idea or too.
1. Definately use the L/H snap starter arrangement, with the black 4.5 X 4 prop. Of course the L/H rotation gives more line tension on take-off & everywhere else, plus that prop w/ the thick tips is really tough. With a L/H prop, a rudder on top will NOW be functional again to help keep the model out on the lines. Perhaps a supply of those larger cox red rubber spinners might be useful to reduce impact shock...but like I said 'a supply', you might go through them faster than normal...
2. The smallest circle radius ( ~26') is safest as a model diving from 26' has less momentum than a dive from 42', of course!
3. Sheet hard balsa wing & tail components will need full length spars.
4. Don't discount basswood either as it makes for really rugged mouse racers.
5. The fuse really needs some thought. Just as I thought 1/4" basswood was the
end all...some junior broke one at the wing t/e joint....hmmm.
6. A flexable (in crash) motor mount is brilliant. Keep working on that!
7.A bit of tip weight will still be advisable.
8. Keep controls on top of the wing where they can anyways be seen.
9. A rubber band spring loaded 1-3/8" mono-wheel would be very good.
OR, a fixed 1/8" music wire LG which might hardly never bend...
That's all I can think of for now , Larry.
I can't wait to see what design you come up with. I sure do know first hand what you're up against!
All the best,
Paul