APC's website has some very interesting information regarding how they arrive at their design shape and size. They basically say they use proprietary computer programs (obviously using formulas like Mark Drela is referring to) to determine the optimum blade shape and size. I wouldn't be surprised if this technology is that different from that used to develop ultra quiet submarine propellors for the Navy. I don't think anyone else even comes close to offering the variety of propellor choices that APC offers - they offer multi-bladed, thick and thin, wide or standard, small to large, electric and powered - quite an investment in mold machining! There's an interesting article on their website right now about developing multi-bladed props for military UAVs. In my mind, to a certain extent, quiet equals efficient equals performance. You'll see with APC props they all share a fairly high aspect ratio tapering to a scimitar tip shape - this is what is most efficient and is more and more being duplicated on full size designs - the new 5 bladed props on the new J model C-130 Hercs being a case in point. Not being an aeronautical engineer, I'd love to know whether theres an advantage in regards to acceleration with blades with a lower aspect ratio and a more conventional square or paddle blade tip shape. With our model airplanes fuel efficiency isn't our top priority and "pull" in aerobatic maneuvering is - I can't help but notice however that Bolly and Mezjlik (spelled correctly?) props are fairly similar in shape to APC and they are favored on the big buck large scale aerobatic jobs... Comments?