In order to address the challenge of accuratelyand rapidly evaluating the aerodynamic interference between rotors in the overall designand flight dynamics modeling of quad-tiltrotor aircraft, a fast analysis method for multirotor aerodynamic interference based on the vortex tube wake model is developed. Based on the classical vortex theory, the wake vortex system of each rotor is abstracted as a semi-infinite vortex tube, and a semi-analytical solution for the induced velocity at any point in space by rotor vortex tubes is derived. This forms an efficient computation method for aerodynamic interference between multirotor. Combined with the dynamic inflow model accounting for rotor self-induced velocity, an accurateand efficient model for calculating the induced velocity in multirotor is established. Based on this, the model is validated using wind tunnel test results of thrust-power performance curves for coaxialand tandem rotors. Finally, the aerodynamic interference characteristics between the four rotors of a scaled model of a quad-tiltrotor aircraft are analyzed during the helicopter modeand tilt transition mode. The results show that the model can capture the influence of verticaland horizontal spacing on aerodynamic interference between rotors relativelyand accurately, making it suitable for fast analysis of multirotor aerodynamic interference. The aerodynamic interference characteristics between rotors near the helicopter mode of quad-tiltrotor aircraft vary significantly. A reasonable aerodynamic layoutand rotor rotation direction design can effectively improve the induced velocity of the disturbed rotorand the load distribution on the rotor disc.

To address the challenge of strong aerodynamic interference in multi-rotor electric Vertical Take-Off and Landing (eVTOL) aircraft and the difficulty of quickly and efficiently analyzing its impact on flight performance and flight quality, an Urban Air Mobility (UAM) flight dynamics model integrated with multi-rotor aerodynamic interference is developed. First, by combining classical vortex theory and dynamic inflow model, a dynamic inflow model suitable for flight dynamics analysis of multirotor is established, accounting for the effects of coupling between rotor flapping and rigid-body motion, thus forming a flight dynamics model that incorporates multirotor aerodynamic interference. Then, the accuracy of this model is validated through comparison with data from international literature, and the impact of multirotor aerodynamic interference on the equilibrium characteristics and required power characteristics of the aircraft is analyzed. Finally, a small-disturbance linearized model is used to study the effect of multirotor aerodynamic interference on the stability of the aircraft. The results show that aerodynamic interference between rotors mainly affects the flight performance and handling qualities of the aircraft in low- to medium-speed flight conditions. Aerodynamic interference slightly reduces the required power of the front rotors while significantly increasing that of the rear rotors, substantially altering the aircraft's longitudinal control characteristics. Multirotor aerodynamic interference significantly enhances the speed and yaw static stability during hover/low-speed flight and improves the lateral static stability in medium-speed flight; however, it causes the angle-of-attack static stability to become unstable, leading to a deterioration in dynamic stability for the heave and spiral modes.

To meet the application requirements of helicopter special situation simulation, a rotor vortex ring state inflow model is established for flight mechanics analysis. Based on the turning relationship of the helicopter vertical motion damping in the rotor vortex ring state, the joint tip vortex motion equation and the modified rotor momentum theory equation are solved to obtain the critical damping boundary of the rotor vortex ring state. The climb rates and induced velocities of the rotor entering and exiting the vortex ring state are given. Cubic spline functions are used to establish a rotor vortex ring state induced velocity model, and the dynamic delay time of the rotor vortex ring state induced velocity is derived from the evolution relationship of the concentrated vorticity in the vortex ring state. Thus, a unified critical damping boundary for the rotor vortex ring state and dynamic inflow model are formed. On this basis, the rotor aerodynamic load model and the flight dynamics model of the helicopter vortex ring state are established, and the wind tunnel and flight test data are used to verify the model. The results show that the proposed model can reasonably and accurately predict the critical damping boundary of the rotor vortex ring state and the changes of the rotor induced velocity with the helicopter descent rate and forward flight speed. Combined with the rotor aerodynamic load model, the proposed model can accurately predict the changes of the rotor tension and increment of torque coefficient with the helicopter descent rate trend. Comparison with flight test data shows that the proposed model accurately simulates the dynamic characteristics of helicopter vertical damping in the rotor vortex ring state, and is suitable for flight mechanics analysis applications.