Research On Model Design And Aerodynamic Characteristics Of A New Concept Of Variable Diameter Tilt-Rotor

The new-concept variable diameter tilt rotor (VDTR) which has a combined aerodynamic advantage of a large-diameter rotor in hovering flight and a small-diameter rotor in cruise flight represents a key developmental direction of the tilt rotor. However, it is a challenge to investigate the structure design, aerodynamic and dynamic problem considering the complexity of the variable diameter rotor during tilting transition flight. In this thesis, the analytical investigations on the aerodynamic and dynamic characteristics of the preliminarily designed variable diameter model tilt rotor have been made.As the background of work, the advantages of the VDTR have been introduced briefly, and several research methods for predicting the aerodynamic characteristics of the tilt rotor have been described. Then, the situation of investigation about VDTR at home and abroad has been summarized.In Chapter 2, a description on the Peters-He generalized dynamic wake model is made primarily, and an analytical model for predicting the aerodynamic characteristic of helicopter rotors is established by combining the unsteady Leishman blade lifting-line theory, rotor flapping dynamic equations and rotor trimming analysis. Then, the comparisons of the calculated results with available experimental data of H-34 have been performed, and the capability of the present method is demonstrated.Based upon Chapter 2, in Chapter 3, a generalized dynamic wake model including the wake curve effects is established to predict the aerodynamic characteristics of transition of the tilt rotor, and the necessity of considering the wake curve has been verified by predicting the off-axis response.In Chapter 4, a model of VDTR is designed, and the dynamic characteristics of the model are analyzed by using finite element software, as a result, the difference between the VDTR and the conventional rotor has been pointed out.In Chapter 5, an analytical model has been developed for calculating the tilt rotor aerodynamic performance at the conditions of hovering, vertical and cruise flight. By this method, the Figure of Merit and cruise efficiency of the V-22 and XV-15 tilt rotors have been calculated. The comparisons of the calculated results with available experimental data have been made for validation purposes. Additionally, the effects of variable-diameter blades on the tilt rotor hover and cruise performance as well as the blade moment have been analyzed, and some conclusions have been given.At last, the investigation on the aerodynamic characteristics of the VDTR during changing diameter and tilting motion is made based on the modified dynamic inflow model and code, and the rotor thrust, flapping angles and moments are calculated and analyzed. Based upon the analyses, some new conclusions are presented.