RE: Futaba 3305 Servos
These servos can be used for any aircraft application. I am using 5 in an Extra 300S without any problems. Go ahead and use them. They may, however, be a bit of an overkill on a 40 size plane. Have you considered using the 3010's instead? A good torque rating and should be cheaper than the 3305's. It will depend on what you are going to use them on.