However, if you do want a 3 bladed prop for your plane, check Hobby Lobby and the Graupner "Super" series. While I have not used their 3 bladed props, I have used their 2 bladed ones and they work very well with 4 stroke engines. I'm sure you will be able to find one for a .91 4 stroke if that's the size engine you are going to use in your P-39 (Top Flite kit???).