I agree with tattoo. Do not use the HS81 plastic gear servos, unless you want to replace gears every time you get mid-aired. I have had the plastic gears strip even without getting hit. The HS81mg's are much stronger. I have several. HS85MG are even better, but more expensive. This season, I will go with the cheapest standard servos I can find. If they get torn up in a contest, its cheaper to buy brand new ones again instead of sending them in for repair. I bet the hs55 servos would strip even on a throttle if it binds a little. The smallest I would use is the hs81. I do use hs85mg and hs81mg on elevator and ailerons, but I have had them 'magically' quit working.