Improvement of Multi-Rotor Aerial Vehicles Performance Using Reduced-Order Aero-Mechanical Models

Research in Flight and Auburn University are teaming to offer a tool capable of providing dramatically improved aeromechnaical mechanisms for the eVTOL/UAM industry.  These vehicles must be configured and designed in order to operate over different phases (i.e., ascent, cruise, and descent). Moreover, in operation these vehicles are subject to various sources of extraneous disturbances and uncertainties in model parameters. Flight performance, control and power consumption characteristics of multi-rotor vehicles change during each phase of flight. These changes can be attributed to complex aero-mechanical interactions caused by the air flow between the vehicle’s main frame and propellers and interactions between propellers and the environment. Several challenges arise with selecting a judicious representation of the aerodynamic loads during forward flight since the air inflow is predominantly non-uniform across the rotor disk. In addition, the inflow distribution is strongly coupled to the thrust. While the presence of these coupled, complex aerodynamic interactions are known, the majority of the flight simulations and operational ORB's employ data fits (thrust maps) or extremely simple models based on “still” propeller-motor experiments. These simple models consider that thrust and torque are proportional to the square of rotor angular velocity. While “simple” models are shown to be “acceptable” analytical models for predicting performance of rotors during hover flight conditions, in the axial and forward flight (majority of the flight time), such models do not reveal the real performance of the entire vehicle. In fact, in addition to the different thrust and torque values, the most important consequence of using “simple” models is that estimations of the power consumed during the cruise phase of flight are poor. Our early results on modeling and simulation of quad-copters (using more accurate aero-mechanical models) indicate the presence of a Goldiluck region (in terms of the cruise speed), where the power consumption of a rotary-air vehicle is at its lowest. Incorporation of enhanced aero-mechanical models into flight-control systems will substantially impact the range of operation of envisioned multi-rotor vehicles widely used for autonomy and logistics.  Improvement in the aeromechanical / aeropropulsive performance, especially at the conceptual and preliminary phases of design is dependent on fast and accurate aerodynamic load calculations for complex vehicles at the conceptual and preliminary design phases.  Research in Flight has developed FlightStream into a fast, robust aerodynamic solver at a fidelity level which substantially advances the state of designs leaving the early phases of design.  FlightStream is being used by the Army to design UAV's and FlightStream has been used to generate the aerodynamic loads for DARPA programs.  FlightStream will serve as the backbone for generating the aero-propulsive loads for this effort.