Traditional control systems like Nonlinear Dynamic Inversion (NDI) rely heavily on precise mathematical models. While this worked well for conventional aircraft, it falls short in today's complex, fast-evolving platforms—especially those with novel configurations or uncertain dynamics. Inaccuracies in modeling can lead to instability, performance degradation, or complete system failure. Moreover, these systems often struggle to respond quickly to external disturbances or adapt in real time. With aerospace designs advancing and mission demands increasing, a shift toward more flexible, sensor-driven control strategies is critical. Due to these limitations, there is a pressing need to reimagine control architecture—and INDI has stepped into that gap.
In two open-access series survey papers ( DOI: 10.1016/j.cja.2025.103553 ; 10.1016/j.cja.2025.103591 ) recently published in the Chinese Journal of Aeronautics , a research team from the Technical University of Munich and Shanghai Jiao Tong University provides the most comprehensive review to date of Incremental Nonlinear Dynamic Inversion. Part I walks readers through the foundational logic and evolution of INDI—from model-based to sensor-based to hybrid systems—while Part II explores its modern extensions, including actuator-aware architectures and stability-enhancing components. Together, these studies serve as both a deep technical reference and a practical roadmap for the INDI-based flight control design.
Part I of the review traces INDI's conceptual shift from model reliance to real-time adaptability. It introduces measurement-based INDI as a turning point: instead of calculating control inputs from models, the system reads real-world measurements to respond more quickly and robustly. This change allows aircraft to reject disturbances one step earlier than traditional methods—an edge in dynamic or unpredictable environments. Hybrid forms, blending model and sensor data, further enhance accuracy by adapting to flight conditions in real time.
The second part digs deeper into the components that make INDI work. It explains how reference models generate desired trajectories, error controllers guide corrections, and estimation modules synchronize commands with actuator states. New actuator-aware extensions—like Extended INDI and Actuator NDI—compensate for different effector dynamics, a vital feature in platforms like tilt-rotor drones or electric vertical take-off and landing (eVTOL) aircraft. The survey also reviews how INDI-based controllers allocate commands across multiple actuators without compromising system stability, even under saturation or time delay constraints.
Altogether, the two-part survey not only maps the technical terrain of INDI but also highlights its growing maturity, signaling that it is ready for large-scale deployment in aerospace and beyond.
"INDI marks a fundamental shift in how we think about control," says Dr. Agnes Steinert, lead author of the survey. "Instead of designing around what we think the system should do, INDI lets us respond to what the system is actually doing in real time. That flexibility is essential for new aircraft architectures and uncertain environments. With this survey, we wanted to demystify the methodology and offer engineers a practical guide for integrating INDI into real-world systems."
INDI offers a control approach that combines flexibility with inherent robustness, making it particularly well-suited for novel and increasingly complex flight systems such as tilt-wing drones, eVTOLs, and other emerging aircraft configurations. Its ability to adapt to changing dynamics and uncertainties in real time allows stable and reliable control even under challenging conditions where classical model-based methods face limitations. The sensor-based structure of INDI has also sparked interest in other fields, including marine and robotic systems, where similar challenges of modeling complexity and environmental disturbances arise. As the technology matures, INDI is steadily advancing from an academic concept toward practical integration in a wide range of safety-critical applications.
Original Source
Agnes STEINERT, Stefan RAAB, Simon HAFNER, Florian HOLZAPFEL, Haichao HONG. From fundamentals to applications of incremental nonlinear dynamic inversion: A survey on INDI – Part I [J]. Chinese Journal of Aeronautics, 2025, https://doi.org/10.1016/j.cja.2025.103553.
Agnes STEINERT, Stefan RAAB, Simon HAFNER, Florian HOLZAPFEL, Haichao HONG. Advancements in Incremental Nonlinear Dynamic Inversion and its Components: A Survey on INDI – Part II [J]. Chinese Journal of Aeronautics, 2025, https://doi.org/10.1016/j.cja.2025.103591.
About Chinese Journal of Aeronautics
Chinese Journal of Aeronautics (CJA) is an open access, peer-reviewed international journal covering all aspects of aerospace engineering, monthly published by Elsevier. The Journal reports the scientific and technological achievements and frontiers in aeronautic engineering and astronautic engineering, in both theory and practice. CJA is indexed in SCI (IF = 5.7, Q1), EI, IAA, AJ, CSA, Scopus.
