My club's field hosts the SAE contest usually, but not this year due to a relocation. FWIW, I see lots of over engineered planes that have very elegant ideas that simply couldn't be implemented right in time for the contest. With that in mind I have to ask: have you tried all of the commercially made props that you can? APC, Master Airscrew, Zinger, and a few others put a lot of time and effort tweaking every aspect of their designs trying to put out a slightly better product than their competitors. By the prop size you're talking about I imagine you're in the class that uses the OS .61? Before spending time reinventing the wheel and putting a prop on your engine that may not even be safe, I'd go spend $20 or so trying every suitable prop that your hobby shop has to see which of those is best. Then if you still want to make your own, you at least have a baseline to compare your work to.