Switch_639,

dont scare that engine with your prop selection.

No jsut kidding!. Like Minnflyer said the manual recommensd 16x8-10. By rule of thumb, you can get 16x8 or 17x7 or 18x6. You need to note that the larger engine rev slower so need more pitch in the prop. So, for example, if you want to 3d on a 55ax, then a 13x4 would be ideal. I found through experience that on a 75AX that would be 14x4 to 14x6 and on FS91SII that would be 14x6-8. On a 95ax that would be 15x6 and on a 120ax it would be 16x8 or 17x7 if there is such a prop. Of course, this will change with prop, airplane and altitude but just a guide.

A fellow filer at my field is flying a Phoenix Yak 60 with the 120AX and a 16x8 prop and I noticed he is not able to maintain elevation in hover- his airplane keeps rising inspite of throttle management. But then again thats a 60 size airplane with a 120ax!

16x4 is too small for the 120ax, if you are looking for a 3d prop, try a 18x4 though I dont think that would make much of a difference, it will give a very low cruising airspeed


Ameyam