Comprehensive evaluation method for lifting characteristics of electric multi-rotor UAV for plant protection

Abstract: With the rapid development of agricultural aviation, electric multi-rotor unmanned aerial vehicles (UAV) for planting protection are favored in plant protection operations due to their advantages of vertical take-off and landing, air hovering, and easy operation. However, because of its low aerodynamic efficiency, there are currently problems such as low loading mass and short battery life, and it is still necessary to optimize and improve it. The lift characteristics is one of the important parameters for the performance test of the multi-rotor UAV. However, few tests have been conducted on the lifting characteristics of multi-rotor UAV. How do we comprehensively evaluate the lifting characteristics of various types of multi-rotor UAV and make comparisons and judgments on the performance of multi-rotor UAV. At present, there are no standards to follow. Only by clearly defining the evaluation index for lift performance, and by standardizing the test methods and evaluation criteria, the performance of the multi-rotor UAV can be judged and the suggestions for optimization and improvement can be given. Based on the existing research results, this paper considered the functional effectiveness criteria of helicopters combining economy, weight reduction, and heat transfer. A method of test and evaluation for the lift characteristics of the semi-tethered multi-rotor UAV is proposed. It includes performance testing semi-tethered platform, lift characteristics test method and index, and lift characteristics evaluation method. In order to verify the feasibility of the method, the performance test of 3 different models (four-rotor, Type I; six-rotor, Type II; and eight-rotor, Type III) was carried out. The test results show that the 3 models have great difference in power load, weight efficiency and thermal efficiency ratio. Type III is the best in power load, 7.6 mN/W larger than the worst Type I. The best Type II is 0.33 larger than the worst Type Ⅱ in weight efficiency. The best Type III is 10.5 N/℃ larger than the worst Type I in thermal efficiency ratio. It reflects the difference in motor and propeller selection and structure of the 3 models of aircraft during the design process, thus showing difference in the performance of the whole machine. On the basis of the above index test, combined with the mathematical model of multi-rotor UAV power system, a scoring method is put forward to evaluate the lift characteristics of the multi-rotor UAV using the power load, weight efficiency and thermal efficiency ratio. The results of the comprehensive score of the 3 types are as follows: Type III > Type I > Type II. The results show that the proposed evaluation method can effectively evaluate the lift characteristics of different types of multi-rotor UAV. It can more objectively and accurately assess the technical level of multi-rotor UAV and strengthen the management of multi-rotor UAV in use. The test and evaluation method presented in this paper can not only be used to evaluate the performance of the multi-rotor UAV, but also provide a reference for the further improvement of the model performance. Of course, in the performance evaluation of multi-rotor UAV, the improvement of power load, weight efficiency and thermal efficiency ratio cannot be excessively pursued, and the balance of technical performance, reliability performance, safety performance, and economical efficiency should be upheld.