Wind field measurement for supplementary pollination in hybrid rice breeding using unmanned gasoline engine single-rotor helicopter

Abstract: The unmanned helicopter has been widely used in agricultural plant protection because it is operationally flexible and does not require a special airport. To achieve full mechanization in hybrid rice breeding, it is necessary to expand the planting width of the male and female parents of hybrid rice. The wind made by the helicopter rotor can spread the paternal pollen farther, making it possible to achieve full mechanization in hybrid rice breeding. There are close relationships among the seed setting rate, operating efficiency, cost-effectiveness, and the parameters of the unmanned helicopter flight, including the wind speed, wind direction and wind field width. However, studies are scarce in this area so far. To explore the optimization parameters while the unmanned helicopter conducts supplementary pollination, including flight altitude, operating load, and operating heading, in this study a wireless wind speed sensor network measurement system (WWSSN) was used to measure the wind field of an Unmanned Gasoline Engine Single-Rotor Helicopter (UGESRH). The flight speed of UGESRH was set to 3 m/s, the operating load was 3.75 kg, and the flying heights tested were 9, 8, 7, and 6 m respectively. The measured wind directions of the WWSSN included parallel to the direction of male parent ridge (X), perpendicular to the direction of male parent ridge (Y), and the vertical direction (H). The test results showed that the wind speed value is VX>VY>VZ, and the wind in direction X is more useful to the supplementary pollination. As the flight altitude decreased, the width of the wind field increased; at operating heights of 6-8 m, the maximum wind field width at wind grade 3 was more than 9 m; when the operating height reached 9 m, the wind field width at wind grade 3 decreased to 4 m. Considering all the various factors together, including the operating efficiency and flight security, a flight height of 7 m is suggested based on the UGESRH-Z3 model unmanned helicopter that we used. The test results also showed that the critical forward wind speed is very small when the UGESRH operates in a headwind, compare with its flight at the downwind direction. Therefore, operation in a headwind is not suggested while using UGESRH to conduct supplementary pollination.