A method for evaluating the helicopter flight quality with external sling loads based on the frequency domain

The helicopter transportation with external sling loads is one of the main transportation modes, which fully reflects the unique flight advantages of helicopters. The helicopter flight quality with external sling loads is the key factor for helicopter tasks. At present, the assessment of helicopter flight quality with external sling loads mainly refers to the qualitative evaluation by the task subjects on ADS-33E. And there is no clear quantitative standard to evaluate the characteristics of a helicopter with external sling loads, making it difficult to accurately quantify the helicopter flight quality with external sling loads. To further improve the accuracy of evaluation on the helicopter flight quality with external sling loads, we proposed a method for evaluating the helicopter flight quality with external sling loads based on the frequency domain, combined with the result of the helicopter flight test and foreign research results. Through numerical analysis and flight tests, we investigated the physical significance and influencing factors of frequency domain indicators for a helicopter with external sling loads. The results indicate that the method based on the frequency domain can more accurately reflect the aerodynamic characteristics of helicopter external sling loads in flight tests. It provides evidence for evaluating the helicopter flight quality with external sling loads and guides the helicopter flight tests with external sling loads.