I used a 15x4 master airscrew k series and it was wonderfull, a 14x4 apw wide blade was awsome two, these were both 61 fx's. 1 in a tango and 1 in a funtana 50, awsome vertical, a note on the 15x4 mas, that prop loads it good but I used to tune mine while holding the plane verticle, all I can say is WOW,