Multicopter propellers


10x5 and 8x4 multicopter propellers.

I have only been flying my multicopter with 10×5 propellers that I bought from Minsoo Kim. Today I was testing out some smaller propellers to see how it would affect the multicopters flying behavior. In theory a large propeller will spinn slower and make the multicopter respond slower but provide more thrust, while a smaller propeller will spinn faster and make the multicopter more responsive.

I bought a pack of 8×4 GWS propellers from Hobby King. The motor I use is the 2213N 800kv (with Plush 18 A ESC)  also from Hobby King.

Obviously the radius was 20% smaller (8 inch vs 10 inch) so far all good. But the width was only about 50% which makes the propeller way less efficient. I didn’t really expect that big difference.

Because of the smaller size, I had to increase my hovering throttle.

Multicopter hovering throttle

This propeller was way too small for my multicopter. With the 10×5 the multicopter hovers at about 40 % throttle. With the new 8×4 propellers the multicopter hovers at 60-70% throttle which is way to much.

It is essential for the flight controller (kk multicopter) to have the ability to stabilize the multicopter by increasing and decreasing the throttle on the motor pairs. Therefore you don’t want your hover throttle to be too high. Let’s say you would have your multicopter hovering at  95% throttle. The flight controller, and you, would then only have +/- 5% margin to maneuver and stabilze the multicopter while hovering, and even less margin while climbing.

3-blade vs 2-blade propellers

I have done some research in forums about 3-blade propellers for multicopter. The main advantage is the smaller radius, which makes it easier to not touch the ground with the propellers. The smaller radius will also let you build smaller multicopters. The disadvantages is that they are more expensive, heavier and slightly less efficient. People say they get less time in the air with 3-blade propellers.

When comparing a 3-blade propellers performance with a 2-blade propeller, a rule of thumb says you should add one inch to the radius and take one inch from the pitch, so a 9×5 3-blade propeller has about the same performance as a 10×4 2-blade propeller.

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