I wouldn't get a Cub to train someone on. Compared to a trainer the Cub is a terribly finnicky flyer. It can be tricky to take off. It flys better slow than fast. It has to have just the right speed for landing or it will suddenly trun into the dirt without warning, and forget fun stuff like flying inverted. It will do it, but again it doesn't like it. If you want really durable that flys ok then look at the Kombat but its not really a balsa plane. If you want a large balsa trainer that comes as kit or Arf and will fly well on a 40(but get a 46 for tall grass) then look at a Sig LT40. The plane turns into a slow glider if the engine quits and is easy to get back to the runway. I used to hang my LT on the prop at 1/2 throttle with an FX40 engine. Then throttle up and start climbing. The LT is also built very strong. I watched one go into a fence at the end of the runway. Other than some broken rubber bands and the broken prop, there was no other damage. My club survey also showed that the LT got the newbies to solo faster than any of the other trainers. The big bird will also land at a fast walking speed. Sig makes a smaller version called an LT25 that is also a great flyer but its a tail dragger which will require a bit more training time. The T34 that someone mentioned would also fit the bill.