The Parametric Aircraft Noise Analysis Module - status overview and recent applications

The German Aerospace Center (DLR) is investigating aircraft noise prediction and noise reduction capabilities. The Parametric Aircraft Noise Analysis Module (PANAM) is a fast prediction tool by the DLR Institute of Aerodynamics and Flow Technology to address overall aircraft noise. It was initially developed to (1) enable comparative design studies with respect to overall aircraft ground noise and to (2) indentify promising low-noise technologies at early aircraft design stages. A brief survey of available and established fast noise prediction codes is provided in order to rank and classify PANAM among existing tools. PANAM predicts aircraft noise generated during arbitrary 3D approach and take-off flight procedures. Noise generation of an operating aircraft is determined by its design, the relative observer position, configuration settings, and operating condition along the flight path. Feasible noise analysis requires a detailed simulation of all these dominating effects. Major aircraft noise components are simulated with individual models and interactions are neglected. Each component is simulated with a separate semi-empirical and parametric noise source model. These models capture major physical effects and correlations yet allow for fast and accurate noise prediction. Sound propagation and convection effects are applied to the emitting noise source in order to transfer static emission into aircraft ground noise impact with respect to the actual flight operating conditions. Recent developments and process interfaces are presented and prediction results are compared with experimental data recorded during DLR flyover noise campaigns with an Airbus A319 (2006), a VFW-614 (2009), and a Boeing B737-700 (2010). Overall, dominating airframe and engine noise sources are adequately modeled and overall aircraft ground noise levels can sufficiently be predicted. The paper concludes with a brief overview on current code applications towards selected noise reduction technologies

Tilt-Wing Control Design for a Unified Control Concept

Urban Air Mobility (UAM) promises an economic and ecological solution for the growing mobility demand by utilizing Electric Vertical Take-off and Landing Vehicles (eVTOLs). Tilt-wing eVTOLs (e.g., Airbus A3 Vahana) appear to be the most promising ones because they offer an efficient wing-borne cruise flight while reducing the need for ground-based infrastructure at the cost of a complex control task. Tilt-wing vehicles increase the pilot's workload and introduce possible human and technical failures due to mechanical complexity. A unified control concept shall be able to handle the vehicle in every phase and provides a single clean and intuitive interface. This work develops a controller capable of decoupling the physical couplings of the flight dynamics. An integrated six-degree-of-freedom rigid body model in a compact mathematical representation is proposed, and flight control requirements are identified. An Incremental Nonlinear Dynamic Inversion (INDI) controller is designed which fulfills the requirements. Moreover, multiple command filters and outer-loop controllers are designed to handle different control modes and provide a proof-of-concept for a unified control scheme. Finally, the closed-loop system is evaluated by means of the control requirements and a generic UAM mission. The closed-loop system masters all parts of the mission and fulfills these requirements. The developed dynamic model and control system will be valuable for future tilt-wing eVTOL research, especially subsequent works on unified control systems

Flight Testing Total Energy Control Autopilot Functionalities for High Altitude Aircraft

In this paper the design and flight testing of a Total Energy Control System (TECS) autopilot for a High Altitude Long Endurance (HALE) aircraft is presented. Autopilot control for HALE aircraft is a well-fitting application for the TECS control strategy, as this enables energy-efficient, decoupled airspeed and flight path control with explicitly handling thrust limitation. To achieve a realistic validation of the controller before moving towards the integration on the HALE platform, the flight testing is carried out on a Cessna Citation passenger aircraft. It has been proven that the adjustments required to implement the control laws on the Cessna Citation passenger aircraft are minimal. This indicates that the Cessna Citation aircraft serves excellently as a hardware platform and can be utilized for the validation of flight control code integration and functionality. The results of the flight test are discussed, and insights gleaned for the future integration of TECS on the HALE aircraft are provided

Dynamic Modeling and Analysis of Tilt-Wing Electric Vertical Take-Off and Landing Vehicles

Electric vertical take-off and landing (eVTOL) aircraft enable new transport options in regional and urban air mobility. One promising but only little investigated and understood subcategory comprises tilt-wing eVTOLs. They offer high efficiency and long flight ranges but come with a trade-off in increased complexity. Consequently, a critical step towards market entry is the development of mature and safe hybrid pilot-autonomy control systems, including fault detection, identification, and recovery (FDIR) concepts. That requires a mid-fidelity dynamic model with sufficient accuracy, which is not yet available despite a long history of tilt-wing research. Without a representative model, no detailed analysis and identification of a trimmed transition trajectory could be performed. This, however, is a crucial step in the development of a control system. We approach the problem by applying and combining current modeling approaches. Furthermore, a trim analysis of different flight phases, including the transition, is conducted. The identified model lays the foundation for a representative and detailed development and investigation of future control designs, bringing tilt-wing eVTOLs closer to airworthiness

Design and Verification of a Linear Parameter Varying Control Law for a Transport Aircraft

This paper presents the design, implementation and simulator verification of inner loop control laws based on linear parameter varying controller design techniques for a CS-25 certified fly-by-wire test aircraft. The synthesis method provides, in contrast to standard gain scheduling techniques, stability and robustness guarantees over the whole defined parameter envelope. Furthermore, it includes the design of the scheduling already in the synthesis process and avoids its a posteriori design. For the controller design, grid based linear parameter varying models of the longitudinal and lateral motion of the aircraft are generated. The longitudinal motion is augmented with two different reference tracking modes: load-factor and pitch rate command. The two control laws are compared in flight by the pilot to validate the handling qualities. The lateral motion control law features a rate command / attitude hold behavior, similar to schemes commonly used in fly-by-wire transport aircraft. Results from a simulation based verification campaign using DLR’s 6 degree of freedom Robotic Motion Simulator are presented as final results in this paper. The simulator verification was conducted as preparation for flight tests of the designed control laws on a Cessna Citation II (550) aircraft

Modular scalable system for operation and testing of UAVs

Abstract-In this paper we present a system for operation and testing of different UAVs. The system allows easy development and modification of control and mission software. The system is composed of hard-and software modules with a standardized interface. We have been using the system with rotary and fixed wing UAVs with a take-off mass between 10 and 100 kg. For larger platforms the system can be used in a redundant setup. The software modules are integrated in a special real-time framework, which supports execution, scheduling, communication and system monitoring. A modular simulation and control infrastructure allows for flexible, integrated design and analysis of control laws. The code for the computational part of the modules can be generated from Matlab/Simulink-models or from Modelica-models. The system supports debugging, soft-and hardware in the loop simulations, operator training as well as real flight experiments. The main design concepts are explained at hand of our solar powered high altitude platform ELHASPA and the 10 years experience in development and operation will be summarized

Symbolic and numerical software tools for LFT-based low order uncertainty modeling

One of the main difficulties in applying modern control theories for designing robust controllers for linear uncertain plants is the lack of adequate models describing structured physical model uncertainties. We present a systematic approach for the generation of uncerteinty models described by linear fractional transformations (LFTs) and report on recently developed symbolic and numerical software to assist the generation of low order LFT-based uncertainty models. The kernel of the symbolic software is a Maple library for generation and manipulation of LFT models. Additional numerical tools for order reduction of LFT models are based on MATLAB and FORTRAN implenmentations of numerically reliable algorithms. Three examples of uncertainty modeling of aircraft dynamics illustrate the capabilities of the new software to solve high order uncertainty modeling problems