Stability and control sensitivity of a lift-plus-cruise eVTOL aircraft to trim strategy and modeling parameters
Résumé
This paper presents an evaluation of an eVTOL configuration to provide insight into the stability of the design, depending on the trim strategies used, and accounting for the impact of interactions. The particular eVTOL configuration is an overactuated Lift-Plus-Cruse platform, and the paper focuses initially on examining trim and stability for different sets or groups of control inputs. Control strategies include power-optimal trim, pitch-level trim, low-speed "helicopter mode" and high speed "airplane mode". Primary considerations and tradeoffs between power optimal trim during transition and more controllable trim is attributed to the thrust sensitivity of the RPM controlled rotors. Two different models are used in the trim and stability studies; a low-fidelity flight dynamics analysis with built-in optimization capability, and a medium-fidelity comprehensive analysis. The paper also includes an initial examination of aerodynamic interaction between the wing and the lifting rotors. The impact of wing interference is primarily to increase the down-wash on the rear lifting rotors, which increases the power requirement and reduce the stability of the short period oscillatory mode.
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