Originally Posted by eflightray
Efficiency is a tricky word in my opinion.
Is it motor 'efficiency', i.e. power in to power out ?, (may have to be measured on a dynamometer).
Or is it 'efficiency' of the flight, i.e. the maximum flight duration.?.
What if the motor was quite efficient, but the model wasn't ?, or the model was quite efficient at flying, but the motor was the wrong one for the required flight ?. I gave those rough %s of loading in the op to deal with these questions, I hoped they would be sufficient?
As I said, to me efficiency is a tricky word when related to model aircraft.
It's efficiency of the whole system, battery, wires, ESC, motor, prop - which should roughly equate to efficiency of the flight I assume?
Originally Posted by Lnagel
There is no comparison. Going from a 12x8 to a 12x6 on 4s will decrease your pitch speed to 75% with a modest drop in power consumption. There will also be some decrease in propeller efficiency. But any change in the airplane's performance, which will be slight but noticeable, can be attributed more to the decreased power consumption and pitch speed.
However, going from 4s to 3s with the same propeller will cause a drastic decrease in power consumption and airplane performance. The motor's RPM, and thus the propeller's RPM, is proportional to the input voltage. A propeller's load, and thus the motor's power consumption, is proportional to the change in RPM cubed. Therefore, going from 4s to 3s will decrease your RPM to 75% of the 4s RPM. This means your power will be reduced to approximately 42% of the 4s level.
You will definitely notice a difference in airplane performance.
Well, the added power of the 12x6 will mostly be relevant during acceleration, and it should slightly reduce the difference in speed between the thrust speed and the plane speed.
This is interesting and worth exploring (but I think you have covered it in almost as much detail as you can with so little information already).
But what about in a situation of same speed, or both at full throttle? If both were at full throttle the 12x6 I believe would go slightly, slightly faster in steady state. It would also get to that speed faster. But what about at the same speed? Which would be drawing more current to go at X km/h in steady state? I think that is an interesting question.
What about both at 50% throttle? Would that be appreciably different to the relationship when both are at 100%? Etc.