Key points of aerodynamics of the propeller of fixed-wing unmanned aerial vehicles

The aerodynamic key points of the propellers of fixed-wing unmanned aerial vehicles mainly include the following aspects:

First, the working principle of the propeller

The working principle of the propeller can be analyzed from two perspectives: momentum and aerodynamics:

Momentum Angle analysis

The rotational plane of a propeller is called the propeller disc surface. The propeller does work on the air flowing over the propeller disc surface, and the momentum of the air increases after flowing over the propeller disc surface.

The accelerated air will exert a reaction force on the propeller, and this reaction force is the thrust of the propeller.

Aerodynamic Angle analysis

A propeller can be regarded as a rotating wing, and its aerodynamic principle is the same as that of an wing.

The section of a propeller perpendicular to the pitch direction is an airfoil, known as the propeller blade element. Each blade element generates aerodynamic force, and the combined force of all blade elements is the aerodynamic force generated by the propeller.

The component force of this aerodynamic force along the flight direction is the thrust of the propeller, and the moment of the component force along the rotation direction relative to the rotation center is the torque of the propeller.

Second, the geometric parameters of the propeller

The geometric parameters of the propeller have an important influence on its aerodynamic performance. The main parameters include:

Propeller diameter D

The diameter of a propeller refers to the diameter of the circle drawn by the tip of the propeller. Generally speaking, the diameter of a propeller needs to be determined comprehensively based on the engine power, rotational speed, flight speed of the unmanned aerial vehicle, the number of blades and the pitch.

The larger the diameter, the greater the area of air that the propeller can sweep through during rotation, and thus the greater the thrust it may generate. However, a diameter that is too large will also increase the weight and resistance of the propeller. Therefore, it is necessary to optimize the design according to the specific requirements of the unmanned aerial vehicle.

Number of blades:

The number of blades is another important parameter of the propeller. Common propellers include 2-blade propellers, 3-blade propellers and 6-blade propellers, etc.

The more blades there are, the greater the maximum power that the propeller can absorb, but the efficiency may decrease and the weight will increase accordingly. Therefore, when choosing the number of blades, factors such as engine power and flight requirements need to be comprehensively considered.

Pitch:

The pitch of a propeller refers to the distance it advances before rotating in a fixed medium for one year. The pitch is determined by the blade Angle of the propeller.

The size of the pitch will affect the thrust characteristics of the propeller. The larger the pitch, the greater the thrust that the propeller can generate during rotation may be, but at the same time, it will also increase the resistance and load of the propeller.

Blade Angle

The blade Angle is the Angle between the chord of the propeller and the propeller disc, also known as the pitch.

The size of the blade Angle will affect the aerodynamic performance of the propeller. In order to achieve good performance at different flight speeds, some propellers are designed with variable pitch so that the blade Angle can be adjusted as needed during flight.

Blade width and thickness:

The width (string length) and thickness of the propeller blades are also important geometric parameters of the propeller.

The distribution of blade width will affect the efficiency and thrust characteristics of the propeller. Generally speaking, the chord length in the middle area is greater than that at the tip and root of the propeller to enhance the overall efficiency of the propeller.

The thickness of the blades should be reduced in weight as much as possible while ensuring strength. The thickness of a propeller usually decreases monotonically from the root to the tip of the propeller.

Third, the aerodynamic performance of the propeller

The aerodynamic performance of propellers mainly includes the following aspects:

Thrust:

Thrust is the component force generated by the propeller along the flight direction and is one of the most important performance indicators of the propeller.

The magnitude of the thrust depends on factors such as the geometric parameters of the propeller, the rotational speed and the air density.

Absorbed power:

Absorbed power is the energy that the propeller absorbs from the engine or motor, which is used to generate thrust and overcome resistance.

The magnitude of the absorbed power will also affect the efficiency of the propeller.

Efficiency

Efficiency is the ratio of the effective power of a propeller to the absorbed power, reflecting the propeller's ability to convert the energy of the engine or motor into effective thrust.

Improving the efficiency of the propeller can reduce the energy consumption of the unmanned aerial vehicle and extend the flight time.

Fourth, the design and optimization of the propeller

In order to improve the aerodynamic performance of the propeller, meticulous design and optimization are required. It mainly includes the following aspects:

Select the appropriate airfoil:

The cross-sectional shape of the propeller blade element is similar to that of the airfoil. Therefore, choosing the appropriate airfoil is crucial to the performance of the propeller.

The selection of airfoils needs to take into account factors such as flight speed, Reynolds number, and lift-to-drag ratio.

Optimize geometric parameters:

The performance of the propeller can be optimized by adjusting the geometric parameters such as the diameter, the number of blades, the pitch and the blade Angle of the propeller.

The goal of optimization is to increase thrust, reduce drag and improve efficiency.

Conduct numerical simulation and experimental verification:

During the design process of propellers, numerical simulations can be conducted using methods such as Computational Fluid Dynamics (CFD) to predict the aerodynamic performance of the propellers.

Through experimental means such as wind tunnel experiments, the design of the propeller can be further verified and optimized.

Fifth, the matching of propellers and unmanned aerial vehicles

The matching of propellers and unmanned aerial vehicles is also an important factor affecting flight performance. It mainly includes the following aspects:

Thrust requirement:

The thrust provided by the propeller needs to match the weight, flight speed, climb rate and other requirements of the unmanned aerial vehicle.

Excessive or insufficient thrust will affect the flight performance and stability of the unmanned aerial vehicle.

Power system matching

The propeller needs to be matched with parameters such as the power and rotational speed of the engine or motor.

Improper matching can lead to low efficiency or overload of the power system.

Pneumatic layout optimization

By optimizing the aerodynamic layout of the unmanned aerial vehicle (UAV), the interference between the fuselage and the propeller blades can be reduced, and the efficiency of the propeller can be improved.

In conclusion, the aerodynamic key points of fixed-wing unmanned aerial vehicle (UAV) propellers involve multiple aspects such as working principle, geometric parameters, aerodynamic performance, design and optimization, as well as matching with UAVs. By deeply understanding and applying these key points, propellers with excellent performance can be designed to provide a strong guarantee for the stable flight of unmanned aerial vehicles.