A common debate in the drone world is whether a two-bladed propeller is better than a three-bladed propeller, and vice versa. 2 blade props make more sense when speed and efficiency are priorities, and they are commonly employed in lightweight drones with less powerful motors. If you want additional force and flight stability, like with bigger drones, 3 blade propellers are the way to go. In this article, we are going to see a comparison between both types of propellers. And for you to better understand we’ll be talking about the characteristics, advantages, and disadvantages of each of them. We have used a two-blade propeller in our DIY Drone project, you can check it out if interested.
What is a Propeller?
So, let’s start with a simple question: What is a Propeller? A Propeller is mounted on top of each brushless motor. It’s is the most important part of drones like wheels in the car. Without a propeller, drones cannot fly. Propellers come in many sizes and shapes, these may have two or three blades. Every propeller has two important things one is Pitch and the other is the diameter. Propeller’s blades are described by
A * B
Where A is the diameter (in inch) of the blade and B is the pitch (in inch) of the blade.
For example, if the propeller is described by 10 * 4.5 then it's means 10 (inch) is the diameter of the propeller, and 4.5 (inch) is the pitch of the propeller.
Diameter is the distance across the circle made by the blade tips as the propeller rotates or we can say it is the vertical length of the propeller.
Pitch represents the twisted present on the propeller’s blade. It is the distance that a propeller would move in one revolution if it were moving through a soft solid, like a screw in wood or we can say it is the distance, the propeller will be pulled forward after one full rotation. If the propeller’s pitch is 4.5 inch its means after one rotation propeller will move forward 4.5 inches.
Diameter gives area but pitch gives an effective area. If we use a higher pitch propeller for the same diameter, the propeller will generate more thrust and lift more weight but it will also require more power. A high RPM provides more speed and maneuverability but lifts less amount of weight. If we want to fly the drone stably with heavy objects then we should use that motor that manages less revolution but provides more torque for which high pitch propeller should be used. To fly a quadcopter, we need a 1:2 ratio for weight and thrust.
Power (watts) = Kp * D4 * P * RPM3
Where,
Kp = for midsized propellers Kp value is 1.2
D = Diameter of propellers
P = Pitch
Propeller’s position plays important role in the flight of drones. We need to be aware of the shape of propellers because these may look the same but they are not actually the same, they may be mirror images of each other like our hands are mirror images of each other but they are not the same.
Two Blade Propeller
2 blade drone propellers have two blades, as the name says. When all other factors are equal, the mechanical efficiency of a drone's propellers increases as the number of blades reduces, which is why two-blade propellers are more efficient than three-blade propellers. Thrust propels a drone into the air. Thrust allows the drone to overcome drag and its own weight and eventually climb into the sky. While a two-blade prop is more economical, it produces less thrust, making it unsuitable for large drones with powerful engines.
2 blade propellers will perform particularly well on drones where a quick motor reaction is necessary but the complete thrust is not as important. Because ultralight racing drones are so light, the amount of push required is small, and having two-blade propellers will result in higher reaction and speed.
Advantages and Disadvantages of Two Blade Propeller
|
Advantages |
Disadvantages |
|
It has higher efficiency as compared to three blades. |
Two blades propeller makes more noise. |
|
It provides faster speed as compared to three blades. |
There are more affected by wind. |
|
It is more durable than a three-blade prop if your copter is going to be crash. |
Two blades propeller provides less stability as compared to three blades propeller. |
|
Making a foldable design for drones with two blades props is much easier. |
|
Three Blade Propeller
Three blades propeller contains three blades that work together to provide increased thrust. Thrust is important for raising up your drone, and three blades propeller can handle greater weight because of more thrust. Manufacturers frequently employ three-blade props on bigger drones since they have more powerful motors and require a lot of force to achieve lift. Due to the tremendous thrust generated by 3 blade props, they are also more stable, which is why 3 blade prop drones feel more gripping when doing fast maneuvers.
Another feature of three blades propeller is that they can fly smoothly even if they aren't completely balanced. This is in contrast to two-blade props, which must be completely balanced and in excellent condition in order to fly smoothly; otherwise, they will begin to produce unpleasant vibrations when spinning.
Advantages and Disadvantages of Three Blades Propeller
|
Advantages |
Disadvantages |
|
Three blades propeller provides the best balance of efficiency, thrust, and grip. |
It is not efficient as compared to two blades propeller. |
|
Three blades propeller provides a very stable flight and can do quick maneuvers smoothly. |
It is not fast. |
|
It creates very little noise as compared to two blades propeller. |
Three blades propeller is not portable. |
|
It is less affected by wind and blade tips have better tracking with 3 blades. |
These are more susceptible to damage in the crush. |
How to make a 2 Blade propeller function like 3 Blade Propeller
If we have two blades propeller and we want to use three blades propeller for the same system and same pitch. We can calculate the required diameter of three blades propeller by using the Propeller equation.
D * D * D * P *√(N-1)
where D is the diameter of the propeller
P is the pitch of the propeller
and N is the number of blades
For example, we have two blades propeller of dimension (9 * 6) and we want to use three blades propeller for the same system and same pitch then
For given two blade propeller,
D = 9, P = 6 and N = 2 and put values in equation
9 * 9 * 9 * 6 * 1 = 4374 …………………….(1)
For given three blade propeller,
D = ?, P = 6, N = 3 and put values in equation
D3 * 6 * √ 2 = D3 * 8.414 …………………...(2)
Equate both equation (1) and (2)
D3 * 8.414 = 4374
D3 = 519.84
D = 8.04
We can say for the same system we have to use three blades propeller of diameter 8 inches.
Conclusion
In this article, you have seen the advantages, and disadvantages of the two blades and three blades propeller. It is difficult to say which propeller is best as it totally depends on the type of drone you fly, as well as the conditions in which you fly it. Two blades props make more sense if speed and efficiency are important, as they are in racing drones. The drone will then be made lighter and use fewer powerful motors in order for the two blades propeller to work optimally. Three blades props, on the other hand, are better for stability and thrust. Additionally, three blades props will be required to generate the thrust required to lift greater loads. Three blades propellers are also better if you're flying in an area where you'll need to perform multiple fast-flowing turns and need additional grip.
Three-blade propellers are not such famous as compared to two-blade propellers. As you may be aware, manufacturers, regardless of industry, are under pressure to make smaller, more portable things. The drone industry is no different. Manufacturers may easily construct foldable and portable drones by using two-blade propellers. To use 3 blade props on a drone, the drone's motors must be powerful enough to drive the prop. Most consumer drones do not have such powerful motors to use of three-bladed propellers because it increases cost. Also, we noted that two blades are quicker, thus they are the prop of choice for racing drones. As a result, expect to see more two-blade prop drones than three-blade prop drones among consumer drones. Three-blade props have their uses. 3 blade props are the prop of choice wherever stability is required, such as for aerial photography or maneuvering.
