Motivation
While automatic landings of large aeroplanes (CS-25) have been common standard in commercial aircraft for some time, the research focus has shifted to the development of automatic systems for the smaller class of commuter aircraft (CS-23).
With these planes, the danger of inappropriate human control inputs by either inexperienced or unpracticed pilots is higher than with large aircraft controlled by professional pilots. To reduce this risk, supporting control systems and increased automation of these planes yield significant safety benefits. The relevance and topicality of this research manifests itself in an automatic emergency landing system by Garmin that was certified for selected aircraft in 2020.
The goal is therefore the development of control algorithms for reliable automatic execution of automatic landings with small commuter aircraft. The demonstration of the systems with various CS-23 aircraft validates the control methods and inventions.
Research Activities
Automatic landings for small commuter aircraft require advanced control systems that cope with manifold special challenges: These aircraft are more susceptible to environmental impacts like wind and ground effect. For this reason, the control effort for exact tracking of desired states increases. This challenge is often amplified by uncertainties due to varying aircraft configurations in this class deviating for example in their landing gear arrangement. Additionally, accurate analyses of the dynamic system behavior of these aircraft are rare.
Especially during the most critical part of a flight, the landing, relying on support systems from ground-based infrastructure like an instrument landing system (ILS) is only possible on large commercial airports, but CS-23 aircraft are usually operated on smaller airfields. The missing information about height above ground increases the requirements on navigation to ensure safe and accurate landing approaches nevertheless. Furthermore, smaller airfields typically feature more complex approach patterns that require a flexible path planning functionality during landing.
These constraints and challenges require complex and flexible functional control systems. They are developed at iFR with the aim of complete automation of the entire landing operation for small commuter aircraft.
Methodology
The design of automatic landing approaches is of elevated importance due to the fact, that the number of control variables exceeds the number of available actuators. This so called underactuated system prevents the exact tracking of all desired quantities. Specifically, commanded values for airspeed, pitch angle and path inclination are to be set such, that a successful and safe landing with respect to structural load limitations and a desired aircraft attitude during touchdown can be performed. The available actuators for this task are only elevator and thrust command. An approach strategy to resolve this disproportion is to reduce the control task to the limitation of said quantities to a bounded range instead of exact setpoint tracking.
A method that renders the control system robust against disturbances and is mostly independent of knowledge about the aircraft model properties is based on the principle of incremental, nonlinear dynamic inversion. This control approach is investigated at the Institute and enables the design of suitable and generally effective controllers that provide various advantages in comparison to conventional control algorithms with regard to automated landings.
Publications
[1] F. Pinchetti, J. Stephan, A. Joos and W. Fichter, "FlySmart - Automatic Take-Off and Landing of an EASA CS-23 Aircraft," in Deutscher Luft- und Raumfahrtkongress 2016, 2016.
[2]F. Pinchetti, A. Joos and W. Fichter, "Efficient Continuous Curvature Path Generation with Pseudo-Parameterized Algebraic Splines," CEAS Aeronautical Journal, vol. 9, no. 3, pp. 557-570, May 2018.
[3]R. Küke, P. Müller, S. Polenz, R. Reichel, F. Pinchetti, J. Stephan, A. Joos and W. Fichter, "Fly-By-Wire for CS23 Aircraft - Core Technology for General Aviation and RPAS," in Aviation in Europe Innovation for Growth Proceedings from the Seventh European Aeronautics Days—20th-22nd October 2015, London, UK, 2016.
[4] O. Pfeifle and W. Fichter, "Cascaded Incremental Nonlinear Dynamic Inversion for 2D Spline-Tracking with Wind Compensation," (accepted for publication).
Federico Pinchetti
Dipl.-Ing.