another possibility is you got a little out of range. your plane will become erratic when that happens. I t might be hard tottell the diference between out of range and shot down????
have you looked at any of the bllue core or fanfold planes? this type of plane would allow you to have plenty of spare parts around cheap and they do have some trainer plans look around the ELECTRIC forums for ideas. these planes can be small to med size and are fun and easy to make.

check out the JK Aerotech T-52 for only 35 bucks ...you would need different radio gear and motor / battery but would be tough and a good flyer.