If your heli has a tail motor and you bumped the ground, even a fraction of a second, you probubly burnt out your tail motor. Or at least damaged it enough to keep it from reaching top speed.(I've been there) Its hard to tell because it still runs, but it woun't run good enough for straight flight. Thats why tail motors are so cheep and in a while you will become very good at soldering and un-soldering tail motors.(like I use to be befor I switchet to belt drive tail) [8D]