Yeah...I know what you mean about the prop looking small. I had built my Lazy Bee with a little Norvel 15 mounted until I discovered the Gyro Bee would have a tremendous amount of drag and the Norvel just did not have the power needed to fly the auto gyro attachment....those heli blades produce a lot of drag, so I dropped in a Saito Gold Knight .30!!!!!

Getting back to your prop situation....with a small .15 you are limited to what size to use. I usually trade one inch of diameter per digit of pitch. So....not sure if anyone makes a 9X3 prop. That may be solution if you can find it. I know they make a 10X 3 and may want to snip a half inch off each blade.

Attached is my newest Bee with the Gold Knight on her. Working on the Autogyro attachment now. Check out the photo of what it will look like when I finish it! Cant wait!