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Propeller

The world of multirotors is quite new, compared to the world of fixed wing models, and most of the propeller manufacturers have not turn to this segment yet. Because of this, we are forced to use kind of propellers that are not idealistic for the multirotors.

Just note that multirotors’ most often flight state is hovering, while fixed wings’ usual flight state is horizontal flying. Because of this, multis would need propellers with shapes different from the ones used in airplanes.Graupner propellers

 

Main params of props are the size and pitch size, where pitch is defined as a distance in inches that the propeller takes during one 360 degree turn.

Beside these, the material, rigidity and weight of propellers is very important, too. A heavy weight propeller would be turned harder then a lighter one, by the same motor, and that can influence e.g. the stability of the copter.

Regarding the material, we can chose from nylon, glassfiber reinforced nylon, carbon, wood and more. If we need higher rigidity, we choose carbon or glassfiber composites, and if the aim is to have softer props nylon can be a good choice.

Note that propellers are the main factor in generating unwanted vibrations, and the more rigid the prop the more prone is the copter to vibrations.

Regarding the shape, we differentiate them as “slow-fly” (SF) and “electric” (E). The ratio of pitch/size is lower at SF props, and as the name suggest they are used for calm flying with longer flight times.

 

The intake power of the propeller can be calculated like this: Power (W) = Kp * diameter^4 * pitch * RPM^3, where Kp is a static value, that is derivated mostly from the manufacturing technology.

Some well-known Kp values are the following:

  • Top Flite, Zinger, Master Airscrew 1.31
  • APC SF 1.11
  • APC E 1.08
  • thin carbon props, GWS 1.18

 

On multicopters we use CW (clockwise) turning and CCW (counter-clockwise) turning props, so same size but different shaped pieces. The turning direction must be the same for both props/motors. The props are usually placed by having the same direction props on the opposite booms of the multicopter, however the position may differ, regarding to the used flight controller.Propeller rotation directions

 

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