My h9 Cub had some up trust built in had same problems that you are having. added shims too mount so it now has 1 or 2 degrees of down thrust and it now takes off fine. Magum 4 stroke 61 and APC 12/6. Motor is not as strong as OS 52. Hope this helps also others tips on toe in etc. should help. Why do they fly better after they a dinged.