ORIGINAL: hewismayer
Mark everything I post is in word. Spelling and grammar should be correct. Unless I have the propeller custom made. The largest zinger makes is a 32x13. That is what Toni Clark in Germany makes for the Zenoah G38. I am using the 42cc Poulan chainsaw engine. I am trying to recreate what they have done. For the Poulan! Good point on the thrust load on the bearings witch is only 24lbs. I can test that by pulling on the shaft when done. The final test will be on a test stand with a couple of tanks of gas. And when the plane is completed! I will conduct a thrust test with a fish scale tied to the aircraft. But any help is welcome especially form a professional. As it is all new to me!
You can't test the bearings by pulling on them, you need to check the bearing rating to see if they will live while turning RPM. I expect the loads we are talking about are fine, but the bearings are small, too. I am used to much bigger pieces in my work, so my seat of the pants feel is off for these small items. I would use a toothed belt instead of a V, they need less tension and work much better overall.
8400rpm on a Zenoah is fine, they like to spin pretty high rpm and are tuned for that. The 42cc Poulan engine should make more power and torque than a G38. You may be able to use less reduction and not have the engine screaming as much if you want to avoid that.
You may want to look into ultralight props, they are similar sizes and may have more variety available.
Mark