"set the rpm to the normal range" I assume this means that you are running a setup that controls RPMs. How close to the amp draw speck limit is safe and most efficient when running less than full RPMs? When setting lap time is it reasonable to adjust RPMs as well as prop size? Also it is my understanding that the motor unloads some during flight. Is this a lot or a little? Last question. Does a 3 blades prop improve efficiency over a 2 bladed prop" IE. for a fixed lap time will the 3 blade prop draw less current?
I am running a KR Governor which controls the entire flight. All the ESC does is transfer energy from the battery to the motor.
Amp draw on the RSM Black Tiger 3548C motor I am using is 23 amps when the motor is at it's most efficient level of 83%. That equates to a rpm setting of 10,200 with the APC 11x 5.5 reverse pitch prop. Lap time is 5.2 sec using .015 stainless steel 7 strand lines of 62 feet length. I would rather lengthen or shorten the lines to achieve preferred lap times instead of moving the rpm up or down and changing props. Once I have the motor running at it's most efficient level I do not want to change things thereby reducing motor efficiency and using more battery energy.
You are correct that the electric motor "unloads" during flight just like the glow engines do. Best I can estimate is that it increases between 300 -400 rpm (only way to check this estimate for accuracy would be to run an ESC like the Castle Creations that has an internal report feature). Since the KR Governor does a whole lot of nice things like protect the motor from burning up in event of a prop strike and give me what feels and sounds like a 4-2-4 break I do not what to do this.
As far as a 3 blade prop goes having the additional blade means you obtain 1/3rd more pull on the prop compared to a 2 blade prop of the same diameter. Not sure that is going to improve on my current motor runs. It would certainly draw more amps and use more battery energy so that would necessitate a total change in my rpm, prop and line length set up. Not worth the trouble in my considered opinion. Good "Rule of Thumb" is a 2 blade 11" diameter prop is roughly equal to a 3 blade 10" prop. I will use a 3 blade prop if I need a larger diameter than the 2 blade I currently run but I don't have enough ground clearance. John, I freely admit that I am not an expert in the area of props. Perhaps one of our aeronautical engineer members should be consulted. What I have outlined above is based upon my own flight experiences not scientific fact.