If you are an AMA member, go to the AMA archive and do a search on propellers, you will find a wealth of information. 3 or 4 articles on modifying them for speed and 3 or 4 again for making your own propellers from scratch(fiberglass or wood), and tailoring a prop for the application. Problem is, the majority of it is written for .40 size racing engines, a little for giant scale, and another little for electric...but nothing specifically for 1/2a, although it is all more or less applicable. The best articles in my opinion are the ones written by Hal Debolt, if you search for his name in the author heading, you will find them pretty quickly.

Austin