How to choose the most suitable propellers for beginners

To achieve optimal performance from your FPV drone, it is important to have a good understanding of propellers. These are the key components that determine the power, responsiveness, and smoothness of your aircraft. Propellers come in various shapes, sizes, and blade counts, and they attach to the motor hub. Therefore, it is important to choose suitable propellers to ensure your FPV drone performs optimally.

1. Basic principles of propellers

1.1 Overview of components

A propeller is a device that relies on the rotation of the propeller blades in the air to convert the power of motor rotation into propulsive force and can have two or more blades connected to a hub, with the backward side of the blade being a spiral or nearly so. The propeller’s propulsive power at different speeds directly determines the maneuverability of the crossing aircraft, so this component directly determines the properties of the aircraft.

1.2 Range of use

All single-axis and multi-axis aircraft.

1.3 Explanation of terminology

1.3.1 Diameter (D)

One of the important parameters affecting the performance of the propeller. Generally speaking, the diameter increases with the tension and the efficiency increases with it. Therefore, if the structure allows, try to choose a propeller with a larger diameter. In addition, the air velocity at the tip of the propeller should not be too high (<0.7 speed of sound), otherwise there may be a surge, resulting in reduced efficiency.

However, the larger the diameter the greater the rotational inertia, the less maneuverable the aircraft will be and the greater the turning, acceleration, and deceleration capability and drag will be. The smaller the diameter the less pulling force, while the fluid stability will be more complicated and the efficiency will be reduced. So at the moment 5″ ~ 5.2″ is the best size for a traversing machine competition. Take the Meps SPACE SZ4942 Propeller, for example, the 49 is the size of the propeller, 4.9 inches. 42 in SZ4942 means 4.2 inches.

How to choose the most suitable propellers for beginners

How to choose the most suitable propellers for beginners

How to choose the most suitable propellers for beginners

How to choose the most suitable propellers for beginners

1.3.2 Number of propeller blades (B)

It can be assumed that the pull and power coefficients of a propeller are proportional to the number of blades. FPV machines generally use simple two-bladed propellers. In the case of the FPV drone, where the propeller diameter is limited, the number of blades is increased to obtain a good fit between the propeller and the motor.

1.3.3 Solidity (σ)

The ratio of the area of the propeller blades to the area of propeller rotation (πR2). Its effect is similar to that of the number of propellers. As the solidity increases the pull factor and the power factor increase. However, this solidity is not as high as possible, it is determined by the speed and airspeed. The larger the solidity the larger the windward area will be and the stickiness of the airflow will reduce the efficiency. The solidity can also be simply understood as the width of the blade.

1.3.4 Geometric Pitch (H)

Geometric pitch refers to the distance the propeller advances in one revolution when the blade profile angle is zero. It reflects the size of the propeller blade angle and points out the working characteristics of the propeller more directly. The geometric moments of the propeller blade profiles may be unequal. It is customary to use the geometric pitch moment at 70% of the diameter as the name value. For example, the 42 in SZ4942 refers to the pitch. Theoretically, the larger the pitch, the more suitable for high-speed flight.

How to choose the most suitable propellers for beginners

How to choose the most suitable propellers for beginners

1.3.5 Propeller Material

The propeller is a high-speed rotating part. Due to the high speed, a little change in mass can have a great impact on the rotational inertia. Large rotational inertia has a significant impact on the acceleration and deceleration of the propeller. Since the propeller is the part that generates the thrust, if the material is too soft the tip of the propeller will buckle and if the material is too hard it will break easily.

It does not need the high institutional strength of the large propellers above 7 inches, but the requirements for durability and flexibility are far greater than other propellers. At present, PC material is the best material for making propellers of 5-inch or so crossing machines. It is not only light and flexible, but also has a guaranteed structural strength.

1.4 Thrust analysis:

1.4.1 Origin of the modern propeller:

In 1836, the British ship “Archimedes” used a screw propeller, which was a long wooden screw like a screw pump. At the beginning of the test, it sailed at a speed of 4 nautical miles per hour (It can be seen as a solid oversized propeller). Suddenly, an obstacle in the water broke the screw and only a small piece remained. Just as the shipbuilding engineer Smith was overwhelmed with anxiety, the ship unexpectedly picked up speed and reached 13 knots. This incident inspired the shipbuilding engineers, they turned the long screw pump into a short one and then turned the short screw pump into a blade shape, and the propeller was born.

How to choose the most suitable propellers for beginners

How to choose the most suitable propellers for beginners

1.4.2 Propeller thrust:

Looking at the birth of the propeller, we will know that the oncoming airflow in the propeller rotation brings the division of force, which is the first force generated by the propeller. The larger the pitch of the propeller the more it is divided. Some propellers have almost no wing shape and fly by this force alone like the propeller of a 3D helicopter. The board can also move forward when it is tied at the right angle.

1.4.3 Modern Air Propellers

Modern air propellers produce another kind of thrust. The propeller produces this thrust on the same principle as a fixed-wing wing.

You can think of the propeller as a wing, and zoom in infinitely on the propeller each page planing surface is a wing relative to the tangential airflow. The propeller rotates through the airflow, creating a forward pull just like a wing creates an upward lift. This is the second thrust of the modern propeller

4.4 The biggest obstacle to propeller thrust

Just like when you play with water you slide fast and create a vortex or bubble. The biggest problem you face when playing with a fixed-wing is the wing stall. Since the principle of the propeller is similar to the wing, it also faces the problem of stalling.

In simpler terms, all wing designs are based on aerodynamics, which is based on the ability of the airflow to wrap around the wing (to stay close to the wing). If a vortex or bubble is created, the first and second forces of the propeller are out of order and the thrust is greatly reduced.

How to choose the most suitable propellers for beginners

How to choose the most suitable propellers for beginners

2 Equipment selection recommendations

With the thrust analysis done, our goal is set. We want a propeller with more thrust, higher efficiency, and less resistance. The maximum thrust we pursue is directly related to the pitch, and the size of the pitch is related to the oncoming airflow, i.e. the speed of the aircraft. In addition, it is also related to the speed of the propeller. This relationship is the maximum pitch without stalling. But for a motor with too large a pitch, its torque is not only screwed but also can not turn fast.

The selection and design of the blade aerofoil is the core influencing factor of the propeller aerodynamic performance. To get a high-performance propeller, it is necessary to optimize the design of a high lift-to-drag ratio airfoil. The propeller can be thought of as a rotating wing, and a high-lift-over-drag means high pull and low torque. Choosing a fully optimized propeller with a high-performance airfoil can optimize the low Reynolds number aerodynamic performance while meeting the high strength and low weight requirements.

Propeller thrust depends on two forces, the first depends on the pitch, the second depends on the shape of the propeller. If the propeller pitch is small then no force, if the propeller pitch is large the problem of stall will occur. If the propeller shape is good, the efficiency is high, and if the shape is poor, the motor will overheat. This is the difference brought by the nuance of the propeller shape (referring to the shape of the profile).

The ideal propeller we want is:

  • Rotational speed within the effective speed of the propeller, the first force can be effectively played
  • Good shape of the propeller, the second force can be effectively played.
  • Clearly define your flight mode, the comprehensive choice of pitch, and solidity.
  • Reliable material, pay attention to the special requirements of a 5-inch crossing machine paddle.

I need to emphasize the third point, their way of flight. If the FPV is always in high-speed flight, maneuvering a large, competitive state, your propeller can be approximated as the propeller of the racing fixed-wing, you need to choose a narrower propeller, the pitch of some large. If the high-speed flight state less, and need thrust, smoothness, and a good propeller, then choose a thin thickness, a little wider blade propeller. If you are looking for a comprehensive FPV, you should look for a comprehensive propeller. The propeller root is thick, thin propeller tip, and the pitch is large and narrow, the tip pitch is small and wide such as this.

From the article, we can learn that the power and characteristics of FPV are the results of a combination of propeller performance and motor curve. Good propeller + good motor ≠ good power, it depends on the fit.

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