I've had bad luck with HS55 servos in 1/2A glow powered planes. One problem is I don't think the HS55 servos include grommets for isolation from vibration, and I have had more than one fail to work due to some electrical fault that I THINK was probably vibration related. I have also had problems with the servo gears, as others have mentioned, the gears are fragile and easily damaged on landing (no landing gear), or just hangar rash. HS55s are great servos for lightweight foamy electric planes, but not so good with 1/2a glow planes in my opinion. Yes, they will work with 1/2a glow, until they don't, which happens with more frequency than I am willing to accept.

A better choice would be the HS65 line, or even the HS81 servos which are awesome for 1/2A up to .19 to .25 size planes.