well.......when i first got tower fun 51, i had this old O.S. .40 engine and it work great, never had any trouble with it. After a while, i decided to step up to more extreme stunts and need more power but ever since i bolted .46 ABC engine on it, it seemed not good engine for any reason and that engine is main cause of the crash. but now i fixed the fun 51 and has .50 O.S. and i didn't mind the little steep price tag and it works far better.