Framework for Real-Time Closed-Loop Simulation of Advanced Rotorcraft Configurations Using Comprehensive Flight Dynamics Models

This paper presents a real-time closed-loop rotorcraft simulation framework using HeliUM-A, a high-fidelity flight dynamics analysis, and a Simulink®-based flight control system model. Serial optimization and parallel computing techniques are introduced in HeliUM-A to achieve real-time speeds. A customized ordinary differential equation solver with parallel load balancing enables accelerated time marching simulations. Software interfaces are introduced to encapsulate HeliUM-A into a Level-2 S-function Simulink® block. Using standardized Simulink® ports, control inputs, rotor/body states and their time derivatives as well as relevant output quantities are communicated in-memory between Simulink® and HeliUM-A for closed-loop execution. This encapsulation retains the parallel computing improvements in HeliUM-A when executed through MATLAB, Simulink® or through the compiled executable automatically generated by the Simulink Coder. The framework is demonstrated on a coaxial compound scout helicopter with a pusher-propeller. Closed-loop vehicle and rotor responses are compared between two flight dynamics models: a stitched simulation model based on linearized models extracted from HeliUM-A, and the original HeliUM-A model. Time domain and frequency sweep comparisons showed excellent agreement between the stitched and nonlinear HeliUM-A models demonstrating that the new HeliUM-A based closed-loop framework shows expected behaviour. The HeliUM-A bare airframe model can be used to simulate various rotorcraft configurations in edge-of-the-envelope flight conditions, whereas the stitched models are accurate for center-of-the-envelope conditions.