“We develop innovative control algorithms in order to make them fly real manned and optionally piloted aircraft.”

Our Vision and Mission Statement

  • Increase safety for manned & optionally piloted aircraft
  • Affordable, modern Fly-by-Wire (FbW) technology specifically tailored for general aviation and future small and medium aircraft applications
  • Reduction of pilot’s workload to achieve significant airworthiness enhancement by beneficial application of innovative active FbW control theory, i.e., effective control augmentation, broadband assistance and protection functionalities
  • Development of certifiable control systems featuring guaranteed stability, robustness and performance properties

Our Approach and Major Objectives

  • Application of novel and robust control theory to flying systems
  • Design to excellent flying qualities and intuitive homogenized handling
  • Specify, analyze, evaluate and validate handling quality characteristics of novel flight control systems and adapt existing methods for handling qualities prediction
  • Pilot modeling, Pilot-In-the-loop Oscillation (PIO) investigation, detection and prevention
  • Close the certification gap and mature modern and robust control techniques for future small and medium manned aircraft, Optionally Piloted Vehicles (OPV) and Remotely Piloted Air Systems (RPAS)
  • Provide evidence according to means of compliance and support certification and clearance of flight control systems
  • Verification and evaluation via pilot-in-the-loop simulation using our flight simulators
  • In-flight functional testing of control algorithms developed using the institute’s flying test bed “Fliegender Erprobungsträger,” a modified hybrid FbW DA42 MPP

DA42 Simulator

How State of the Art FbW Control Technology Can Contribute to Flight Safety

Except for aviation (“flying heavier than air”), there is no automotive application where a “black-out failure” within the control loop “pilot – control system – vehicle” inevitably causes such dramatic consequences. Hence, the primary objective of every aircraft design and layout is always safety – all other goals and requirements are subordinated to this.

However, the perpetual evolution of modern FbW Flight Control Systems (FCS) during the last decades offers a wide range for optimizing the aircraft regarding its performance and the flight envelope without imposing the previously necessary compromises considering stability and control characteristics by providing excellent, homogenized handling qualities via the (digital) active FCS. Hence, novel configurations that without the augmentation of the (digital) FbW FCS would be uncontrollable or could be handled with greatest effort only, can be adequately flown by the pilot.

Today, the major operational benefits of advanced active FbW FCSs within modern transport and high performance aircraft are undisputable. Due to their broad band of valuable assistance, augmentation and protection functionalities they enable (in particular) a significant reduction of pilot workload, an effective monitoring of pilot inputs along with current flight condition to generate appropriate warnings and/or protections, if applicable, towards the vision of “carefree handling”. In sum, they offer a high potential to increase the airworthiness and thus the passenger, crew and aircraft safety.

Our Objective: Provide More Safety Where It is Needed Most

DA42 OE-FSDNevertheless, such active FbW technology and its worthwhile safety features did not find the way into the General Aviation (GA) sector, although it is standard in modern transport and high performance aircraft. The reason is obvious: the tremendous cost (development, system/hardware and certification) can easily exceed the actual price of the (basic) airframe by several times. This seems all the more tragic in the light of the evidentially much higher accident rates within GA small and medium airplanes compared to common transport aircraft (airliners), which are mainly due to the lower technical standard and in particular to the comparatively poor training level and small number of flight hours of GA versus airliner pilots.

All the more, the innovative active FbW flight control technology with its well-proven, safety enhancing features has to be matured to be affordable for GA and future small and medium aircraft in order to diminish the high accident rates and thereby protect human lives. This embodies our major vision.

Consequently, our control system design and development primarily aims at providing at least the same level of safety increase as common FbW FCS (i.e., excellent handling qualities and pilot assistance), while simultaneously accounting for significantly reduced development, acquisition and operating costs by elaboration of dedicated processes, tools and hardware solutions, enabling the progression of control algorithms which are perfectly tailored to the specific needs of manufacturers of small and medium-sized planes.

Conversely, if a failure occurs within such an active FbW FCS, the configuration drops back to the interaction of the human pilot with the degraded (maybe deteriorated) airframe dynamics and the topic of “controllability” moves immediately back into focus. Hence, a fail operative / fail safe characteristic of this vital system is always required. This leads directly to the fundamental issue of handling qualities as the “ability of balance and steering an aircraft” according to the Wright Brothers’ original definition. In other words, handling qualities directly relate to the ease with which a specific task can be performed by the pilot, i.e., the so-called pilots’ workload. Thus, the circle is closed: by ensuring excellent and homogenized handling qualities for the human pilot in all flight scenarios, we will provide a valuable contribution for safety enhancement within manned aircraft and OPV. This is a central objective of our control algorithm design.

Finally, the substantial coupling effects with the human pilot acting as continuous dynamic control element within the closed “pilot – aircraft – FCS” loop emerges a further, unexpected and often extremely serious handling qualities problem of FbW aircraft, the so-called “nonlinear and high order Pilot-In-the-loop Oscillations” (PIO), which require the application of innovative novel methods for “pre-flight” PIO-tendency detection, evaluation and thus prevention.

Bringing Innovative Solutions Close to Industrial Application

On the other hand, could the pilot of a manned aircraft be supported by active (potentially robust) control if things go wrong? Promising new results from control theory research suggest appropriate solutions. Nonetheless, due to the specific requirements and boundary conditions of the aerospace environment and the totally unresolved certification problem (“certification collapse”) in particular, these new methods are far away from application within production aircraft.

Hence, it is another major vision of our research group to bridge this gap by maturating the modern robust control techniques and to address their robustness and certification capability in order to empower their beneficial application within the FCS of real operational aircraft.

Motivation of the Methods Used

  • Definition/contriving of highly sophisticated controller structures based on in-depth insight into the flight dynamics properties, thus providing optimal structural foundations for robust controller design to excellent handling.
  • Development of methodologies for excellence in handling qualities design by application of innovative, modern nonlinear and robust flight control techniques, e.g., Model Reference & Multi Model Eigenstructure Assignment (MR DEA/MMEA), Method of Equivalent Derivatives, Quantitative Feedback Theory (QFT), Model Reference Adaptive Control (MRAC), Pole Region Assignment, Control Allocation, LQR/LQG, etc.
  • Assessment and proof of evidence of control system stability, performance and robustness;
    LFT uncertainty modeling, Structured Singular Value (SSV), μ– and advanced μΔΓ-Analysis, Robust Compliance Verification
  • DA42 Simulator CockpitLinear and nonlinear pilot modeling for handling qualities analysis and prediction of novel flight control systems
  • Pilot-in-the-loop experiments in the highly realistic environment of our various flight simulators. We are in contact with a large number of pilots with different types of flying experience, who participate in our studies and give us valuable feedback.
  • Simultaneous consideration of functionality, system and control algorithms
  • Probability and requirements conditioned control

Team

Affiliate Professor Dr.-Ing. Matthias Heller, Rudolf Diesel Industry Fellow of TUM-IAS

Selected Publications

[4] F. Zhang, T. Fricke and F. Holzapfel, "Integrated Control and Display Augmentation for Manual Remote Flight Control in the Presence of Large Latency", in AIAA Guidance, Navigation, and Control Conference, 2016. [doi]
[3] F. Zhang, S. Braun and F. Holzapfel, "Physically Integrated Reference Model and Its Aids in Validation of Requirements to Flight Control Systems", in AIAA GNC and Co-Located Conferences, 2013.
[2] F. Schuck, M. Heller, T. Baier, F. Holzapfel, "Longitudinal Robust Controller for excellent Handling Qualities Design of a General Aviation Aircraft using QFT", in AIAA Guidance, Navigation, and Control (GNC) Conference, 2013.
[1] M. Heller, F. Schuck, L. Peter, F. Holzapfel, "Hybrid Control System for a Future Small Aircraft", in AIAA Guidance, Navigation and Control Conference, 2011.

Header Image: A. Heddergott / TUM