11x6 is the correct size for this engine with a trainer,the 10x6 will be too fast if your a new pilot!!.my la 46 has a graupner 11x6 and has plenty of power!!.a smaller prop will be much faster ,more rpm so get a 11x6 for your trainer.did you try the setytings a gave you for the engine?,let me know how it goes and good luck.also a trainer only needs the power of a good 25 to fly so the 46 la is fine!!.just get a 11x6 prop on it!!!.