After flying the 4 star for a few years I wanted to give an update. My first one flew with an OS 26 Surpass and Tactic TSX20 servos. Its a great combo but if built to spec the nose will be very heavy with that engine. SIG suggested moving the firewall back an inch. My second 4 Star20 was built with HS81 servos and a Thunder Tiger GP25. A good snappy combo but I think I like the TSX20 servos better despite the extra weight. The bushing Thunder Tiger(or OS25FP that is also commonly available) is a good match to the airframe for the power to weight. A 15 should pull it along well perhaps a Magnum XLS15? Both the 26 Surpass and the GP25 have power to spare on this plane. I liked the gas mileage of the Surpass combo and the sound.