The best props for scale electric are Vario because you can have both the scale diameter and you can dial in the pitch to suit the target Amp load. There are speed sport and scale blade choices too.
Vario props aside I normally use APC's for everything electric. They are designed correctly for gas glow and electric flight. Dont waste your time on anything else to be honest if your looking for performance. Scale is another issue and I go back to Vario for that.
The way I calculate my set up is to start with 11000RPM and figure out what the motor needs voltage-wise to get there based on its KV. I know ahead of time the motor class and then I choose the KV. I tend to stay on the higher voltage side on set ups. The reason I chose 11K RPM is because I know these systems run at around 80% efficiency so the in flight RPM will be around 9K RPM which is a pretty sweet spot. The props are designed for about 10K RPM and anything more is for high performance set ups as they get more critical as the speeds and RPM go up. There are high speed carbon props for real speed.
Now I know the motor RPM, battery voltage and ESC. Looking at the props in the range of my motors capability I choose the highest pitch I can to get the load right on the bench. Now I compare that data back to the target RPM I was going for which gives me an idea of the efficiency of the actual system compared to the estimates. The final verification is in flight data. I have found my estimates to be very close to the actual performance in flight and the planes have been a lot of fun to fly.
Sudstad you seem to be leaning towards scale so I would direct your attention to the 3 blade Vario Props. Ive used them and own 3,4 and 5 blade hubs.
In terms of scale diameter the full scale prop on a P-38 was 11'6" if memory serves. So to get the right diameter lets figure out the basic scale of this plane, its a 90 inch wing right? The wingspan on the P-38 is 52'0" so 624 inches divided by 90 inches is a factor 6.933 so call it 1/7 scale. The full scale prop dia is 138 inches so divided by 7 is 19 inches.
Pretty sure the motors you are running and a three blade prop like Master are not going to work for a couple of reasons. Poor blade design being one.
It might be a stretch to try and get a 19 inch two blade fixed pitch prop to work let alone a three blade on the motors you have. So your going to have to test and see what the real numbers are to make a compromise on the size.
Once you settle on a two blade dia and pitch then take a good look at the Vario Props and choose a 3 blade hub to fit the motors. You can change out blades cheaply its the hub thats a little bit expensive but then you have it and you can change styles and diameters very easy.
Also keep in mind the highest stress you will put your power system thru is on the bench. The air is static and the cooling is not optimal because there is no boundary layer flow or air pressure from the speed. Things will run cooler and better in the air usually.
Last edited by Chris Nicastro; 08-26-2014 at 08:53 PM.