Ive recently put a gyro on my L39, its a Futaba 351. The model would waggle around at the back end which was starting to irritate me [:@] There was no possible way I could correct this myself during the flight without a gyro on the rudder. I stuck the gain on a slider, mixed it to turn off at gear down (just to be safe). The model is so much better now I cant believe I didn't do it earlier.