The Rev-up 10x4 copies would be a little small I think. I used to use rev-up 10x5, and 11x4 on a 3lb 6oz stick type airplane with the HP.40 with good results. The APC 12.25x3.75 is to much prop for the HP.40. If I was using a larger engine for this airplane it would be ok. To switch to a larger engine would add at least 5oz to the aircraft weight. I don't want increase the weight any more than I have to. My target weight is 3.5lb it should be way over powered at this weight, as the 3lb6oz plane would go up like a rocket. Tom