Semi-Empirical Aerodynamic Modeling Approach for Tandem Tilt-Wing eVTOL Control Design Applications

Abstract

The development of fault-tolerant control concepts for tandem tilt wing aircraft in nominal and non-nominal conditions requires an aerodynamic modeling tool that captures relevant effects while maintaining modeling flexibility. In this work, a semi-empirical approach for aerodynamic modeling with focus on the propeller-wing interaction is presented. As a foundation, two-dimensional aerodynamics of an airfoil in interaction with propellers and flaps are considered. Combining the effects of numerous airfoil sections, the approach is extended to 3D in order to model a complete aircraft by applying strip theory. Finite wing effects on the lift distribution are taken into account. Without reference data for a full tandem tilt wing configuration, validation was performed on each subcomponent individually or combinations of components. The validation tests showed satisfactory agreement with the experimental data. Together with weight & balance and propulsion models, the tool allows performing trim analyses for the complete flight envelope, which is the foundation for finding flight corridor for stable transition flight. Failure cases, like loss of a motor or stuck actuators, and their impact on the flight envelope and transition corridor can be investigated in the future. Besides these analyses, the presented model can also be used for dynamic flight simulation or aerodynamic model identification.

Parameter Tuning Approach for Incremental Nonlinear Dynamic Inversion-Based Flight Controllers

“…The aerodynamic forces and torque are calculated using a component-based aerodynamic model as presented in, e.g., [26,27]. Therefore, the wing and tail of the aircraft are subdivided into aerodynamic elements having a triangular, rectangular, or trapezoidal shape as shown in Figure 6.…”

Dynamic Inversion-Based Control Concept for Transformational Tilt-Wing eVTOLs

“…Pilot interaction is mainly related to the topic of unified control, for instance, applied in [6,8,10], while robust control is of particular interest in urban and close-to-ground operations, where gusts and urban canyons pose unique risks. Failure mitigation of these vehicles is, for example, motivated in [11,12] and of special interest for the transforming element. Furthermore, the different flight regimes with distinct flight dynamics and the transition between them must be appropriately handled.…”

“…In [11,14], several approaches to modeling and simulating the aerodynamic properties of a tilt-wing are shown. Those include the Vortex Particle Method (e.g., DUST), CFD, Doublet/Vortex Lattice Method (e.g., OpenVSP), and semi-empirical approaches (e.g., Strip Theory).…”

“…They provide an accurate though computationally affordable solution to (tilt-wing) aerodynamics. However, the complexity is still high due to the nature of the aircraft configurations, which comprise 20 to 30 different dimensions to vary and require large computations [11,14]. Thus, in the early stages of development, it is more advantageous to employ simpler approaches, such as the semi-empirical strip theory, particularly if the aim is to develop concepts rather than concrete aircraft designs.…”

“…With sensory NDI, we can reduce the relevant dynamics form (6) according to (9), yielding ). Thus, the dynamic inversion objective is to solve (12) for 𝒖 com . The inverse function theorem, and, finally, the implicit function theorem, give information about the (local) solvability of these types of equations: if the stacked Jacobi matrix…”