How propeller size and number of blades affect thrust and efficiency?


I’ve heard a lot of mixed information about how number of blades can affect performance and duration of the flight of your racing drone, so I’ve decided to put my thrust test stand to a good use and test various micro motors I had on hand and different propeller configurations.

Motors
  • 1102 10000kv
  • 1102 7800kv
  • 1104 6500kv
Propellers
  • 2535-2 blades
  • 2535-4 blades
  • 2535-2 blades cut down to 1.88″
  • 2535-4 blades cut down to 1.88″
Methodology

I’ve run each micro racing motor for 3 times with each of commonly used propellers on ~50% throttle and ~100% throttle. For each run I’ve used different battery. Then I’ve picked average result.

Disclaimer

I doubt that data I’ve collected are 100% accurate, so they should be considered with the grain of salt.

1102 10000kv motor

1.88″ propeller with 2 blades (2S battery)


img_6344-1102b-10000kv-1935-2-50


img_6345-1102b-10000kv-1935-2-100

1.88″ propeller with 4 blades (2S battery)


img_6353-1102b-10000kv-1935-4-50


img_6354-1102b-10000kv-1935-4-100

Summary for 1102 10000kv with 1.88″ propellers
Motor Propeller Throttle Amps Watts Thrust g/W
1102 10000kv 1935-2 50% 2.13A 17.1W 21g 1.23
1102 10000kv 1935-2 100% 4.27A 33.1W 35g 1.06
1102 10000kv 1935-4 50% 2.7A 22.5W 22g 0.98
1102 10000kv 1935-4 100% 4.99A 39.5W 34g 0.86

I’ve noticed that when motor was spinning on full throttle with 1935-4 blades propeller there was a bit of burning smell and motor was hot after it. So 1935-2 blades was a clear winner in this case.

2.5″ propeller with 2 blades (2S battery)


img_6359-1102b-10000kv-2535-2-50


img_6360-1102b-10000kv-2535-2-100

2.5″ propeller with 4 blades (2S battery)


img_6364-1102b-10000kv-2535-4-50


img_6365-1102b-10000kv-2535-4-100

Summary for 1102 10000kv with 2.5″ propellers
Motor Propeller Throttle Amps Watts Thrust g/W
1102 10000kv 2535-2 50% 2.7A 22.1W 27g 1.22
1102 10000kv 2535-2 100% 5.09A 39.6W 35g 1.01
1102 10000kv 2535-4 50% 2.68A 22W 22g 1.09
1102 10000kv 2535-4 100% 5.72A 45.3W 34g 0.8

At around 50% throttle 2.5″ 2 blades propeller seems to have advantage over 1.88″ but later on difference in thrust almost disappears which suggests that 2.5″ 2 blades propeller might be the maximum 1102 10000kv motor can handle.
2 blades has clear advantage over 4 blades in this case as well.

1102 7800kv motor (2S battery)

1.88″ propeller with 2 blades


1102-7800kv-1935-4-50


1102-7800kv-1935-2-100

1.88″ propeller with 4 blades


1102-7800kv-1935-4-50


1102-78000kv-1935-4-100

Summary for 1102 7800kv with 1.88″ propellers
Motor Propeller Throttle Amps Watts Thrust g/W
1102 7800kv 1935-2 50% 1.56A 12.9W 20g 1.55
1102 7800kv 1935-2 100% 2.89A 23.2W 32g 1.38
1102 7800kv 1935-4 50% 1.94A 15.9W 19g 1.19
1102 7800kv 1935-4 100% 3.36A 27.3W 29g 1.06

In the case of 1102 7800kv 2 blades seem to have an advantage as well. Efficiency has increased in comparison to 10000kv.

2.5″ propeller with 2 blades (2S battery)


1102-7800kv-2535-4-50


1102-7800kv-2535-2-100

2.5″ propeller with 4 blades (2S battery)


1102-7800kv-2535-4-50


1102-7800kv-2535-4-100

Summary for 1102 7800kv with 2.5″ propellers
Motor Propeller Throttle Amps Watts Thrust g/W
1102 7800kv 2535-2 50% 1.86A 15.3W 28g 1.83
1102 7800kv 2535-2 100% 3.7A 29.3W 43g 1.47
1102 7800kv 2535-4 50% 2.12A 17W 29g 1.7
1102 7800kv 2535-4 100% 4.23A 33.5W 40g 1.19

In case of 1102 7800kv 2535-2 seems to perform better than other configurations.4 blades were still making motor very hot.

1104/5 6500kv motor

1.88″ propeller with 2 blades (2S battery)


1105-6500kv-1935-4-50


1105-6500kv-1935-2-100

1.88″ propeller with 2 blades (3S battery)


1105-6500kv-1935-4-50


1105-6500kv-1935-2-100

1.88″ propeller with 4 blades


1105-6500kv-1935-4-50


1105-6500kv-1935-4-100

1.88″ propeller with 4 blades (3S battery)


1105-6500kv-1935-4-50


1105-6500kv-1935-4-100

Summary for 1104/5 6500kv with 1.88″ propellers
Motor Propeller Throttle Amps Watts Thrust g/W
1104/5 6500kv 1935-2 50% 1.7A 13.7W 26g 1.9
1104/5 6500kv 1935-2 100% 3.51A 27.7W 49g 1.76
1104/5 6500kv 1935-4 50% 2.71A 21.4W 36g 1.68
1104/5 6500kv 1935-4 100% 4.61A 35.8W 54g 1.51
1104/5 6500kv 3S 1935-2 50% 2.74A 32.4W 50g 1.54
1104/5 6500kv 3S 1935-2 100% 5.28A 58.6W 79g 1.35
1104/5 6500kv 3S 1935-4 50% 4.44A 51.3W 63g 1.22
1104/5 6500kv 3S 1935-4 100% 6.62A 73.1W 82g 1.12

1104/5 6500kv motor

2.5″ propeller with 2 blades (2S battery)


1105-6500kv-2535-4-50


1105-6500kv-2535-2-100

2.5″ propeller with 2 blades (3S battery)


1105-6500kv-2535-4-50


1105-6500kv-2535-2-100

2.5″ propeller with 4 blades


1105-6500kv-2535-4-50


1105-6500kv-2535-4-100

2.5″ propeller with 4 blades (3S battery)


1105-6500kv-2535-4-50


1105-6500kv-2535-4-100

Summary for 1104/5 6500kv with 2.5″ propellers
Motor Propeller Throttle Amps Watts Thrust g/W
1104/5 6500kv 2535-2 50% 2.94A 23.7W 47g 1.98
1104/5 6500kv 2535-2 100% 5.18A 39.5W 72g 1.82
1104/5 6500kv 2535-4 50% 3.75A 29.1W 53g 1.82
1104/5 6500kv 2535-4 100% 6.16A 46W 79g 1.72
1104/5 6500kv 3S 2535-2 50% 4.52A 52.8W 81g 1.53
1104/5 6500kv 3S 2535-2 100% 7.33A 79.2W 110g 1.38
1104/5 6500kv 3S 2535-4 50% 5.98A 65.4W 89g 1.36
1104/5 6500kv 3S 2535-4 100% 8.36A 86.7W 103g 1.19

Same as with other motors 1104/5 6500kv motor was hot after spinning 4 blades props and efficiency was slightly lower.

Conclusion

Although I doubt that collected thrust data are 100% accurate and real numbers can be higher or lower, we can still see how efficiency changes depending on with which propeller different motors are used.

Smaller motors are getting hotter with bigger propellers or more blades and don’t offer better performance.

It seemed that four blades were always under-performing with selected motors, but probably it can be different with lower kv 1104/5 motor or bigger motor.

It worth to note that four blades always generated less noise. I’ve also heard that 4 blades can offer better agility. But everything comes with the price and it is a question of the proper balance.

So to conclude 2 blades setup seems to be able to offer longer flight time and more thrust with high kv micro motors for the price of more noise.

Leave a comment