Padeye is correct. Its the airframe that must be scratch-built. All teams competing are required to use the same engine. We will be buying a prop, not builidng one ourselves.
In our previous year we just stuck on the recommended prop size as per the manufacturer. However, when at the competition, several other (more experience, more winning…) teams told us we weren’t using the correct prop. So this year we’re making it a point to do prop tests/research. We’d like to know where to start so we can avoid buying the whole store out…
None of us are experienced RC fliers. We will be hiring a professional to actually do the flying. We’re talking to him too, of course.
I’d try an APC 14X4W on an OS 61 FX for lots of thrust and not much speed. If nothing else it would give you a starting point for your tests. I know you said you didn’t want a direct recommendation, but I think that re-inventing the wheel (or prop as it were) is just a lot of extra work unless you are planning on building your own prop. More people than you realize do make their own props for RC use, several I know of with home made CNC milling fixtures.
In general terms, I’d go with 13 to 14 inches of diameter and 4 to 6 inches of pitch. This will load the .61 down pretty good, but should have it in the near peak torque range for that particular engine.
Don’t ask me where I came up with this…I don’t particularly want to discuss RC here.