RE: HP VT21 worth using?
I have the .21 and .49 and the .25 car engine. They are not super powerful but are quieter than anything available. They idle fine and are quite docile. I use my .49 on a .40 sized photo plane and it is absolutely perfect for a slow flying application. They are so quiet that I had an electric starter on mine and was wondering why it wouldn't start after 5 seconds. I pulled the starter away and it was running the whole time and I couldn't tell! The new ones have roller bearing heads and I've retrofitted all of mine with these. A really neat engine!
Max