Dragonfly Hub Loads Correlation with Wind Tunnel Data

To validate simulation work towards the design of the Dragonfly rotorcraft lander, a process of extracting a modal model from impact test data is described in this paper. Through a curve-fitting process using Siemens Testlab software, modal frequencies, damping, and mode shapes are extracted and mass-normalized to be imported as a modal model into the Rotorcraft Comprehensive Analysis System (RCAS) to represent the dynamics of the underlying structure more accurately. Wind tunnel conditions were simulated to compare to hub loads measured during wind tunnel testing. An initial comparison of RCAS with VVPM inflow and RCAS coupled with HELIOS show similar hub loads but also show the importance of modeling the rotational degrees of freedom of the structure properly. Additional modeling comparisons between modeling the hubs and the load cell locations further illustrate that by capturing rotational mode shapes based on test data, in-plane hub loads are predicted more accurately.