Another thought, a 12 X 10 prop has a lot of pitch and it may be like trying to drive your stick shift car from the curb in high gear, it may take a long time to get enoujgh speed to take off. That is why full scale high performance aircraft have variable/constant speed props. You take off with in your case with a prop like a 13 X 6 (low gear) and then when you get up and in the air you put the prop in high pitch your 12 X 10 (high gear) and away you go. My full scale SNJs (Texans) would barely taxi with the prop in high pitch. I used to use wood props on my 1?4 scale models with gas engines with a variable pitch 18 X 6-10. When the engine was pulling such as on take off it would act like a low pitch and then when in the air and the blades unloaded it would act like a 10 pitch. I believe that Zinger made them. Norm