High-fidelity rotorcraft simulation model: analyzing and improving linear operating point models

The simulation of the helicopter motion is a central component in flight control design, handling quality studies, and the understanding of physical effects. At best, the flight test results fulfill the expectations from the simulation. Even though identification and simulation techniques for linear models were continuously developed in the past, the fidelity achieved with existing tools is still insufficient—based on the experience with the research rotorcraft EC135 ACT/FHS. This paper is about the improvement of the simulation fidelity for the bare and stabilized vehicle. A pragmatic procedure is presented that updates a given linear (physics-based) model by adding (not physics-based) models and systems. Methods used are inverse simulation, partial closed-loop analysis, and model stitching. The paper shows how to combine these methods in a certain framework so that the simulation fidelity is significantly improved. Comprehensible examples as well as data from the research rotorcraft ACT/FHS are documented to provide the reader with more insights.