Lidar-based Wake Identification and Impact Alleviation

Wirbelschleppen können bei einfliegenden Flugzeugen zu gefährlichen Flugzeugreaktionen wie plötzlichen starken Rollbewegungen führen. Die vorliegende Arbeit präsentiert einen möglichen Ansatz für ein Steuerungssystem zur Reduktion der Flugzeugreaktion bei Wirbelschleppendurchflügen. Das OWIDIA (Online Wake IDentification and Wake Impact Alleviation) genannte Steuerungssystem nutzt die Informationen eines vorausschauenden Doppler Lidar Sensors, um ein Modell der Wirbelschleppe zu identifizieren und auf dessen Basis Steuerflächenausschläge zu generieren, die die wirbelinduzierte Störung kompensieren. Dieses Steuerungssystem wird in die gesamte Flugsteuerungsarchitektur eines modernen Fly-by-Wire Flugzeuges integriert und hinsichtlich seines Potentials zur Reduktion der wirbelinduzierten Flugzeugreaktion analysiert. Daraus werden Anforderungen an zukünftige Lidar Sensoren für die Nutzung mit dem OWIDIA System abgeleitet. Die Analysen zeigen ein vielversprechendes Potential des OWIDIA Systems. Mit geeigneten Sensorkonfigurationen kann es den maximalen Hängewinkel bei typischen Wirbelschleppen-durchflügen im Landeanflug um durchschnittlich ca. 70 % reduzieren

Towards Mission Readiness – Applying the Objective Motion Cueing Test to the Apparent Vertical Filter

Flight training simulators have a limited capability to replicate aircraft motion cues because the space envelope of current motion systems mpedes a better fidelity and urges the user to make sometimes painful ompromises. Therefore, it is all the more important to use the given space envelope as well as possible. But this trivial consideration yields an answer to the question what “good” means and therefore what strategy shall to be pursued by a control algorithm. For the Apparent Vertical Filter (AVF) this eans that the amount and direction of the force combined with the orresponding rotational velocity shall be met as long as the given space nvelope allows that approach. If this is not possible anymore the direction of the specific force shall be reproduced correctly. Only if both, the rotational and the translational cueing cannot be achieved a decision must be made. This is the case e.g. for the side force during a taxi turn on round. During such maneuvers a compromise needs to be found between a correct specific force and a limited rotational velocity of the simulator. Within this paper the working principle of the Apparent Vertical Filter will be discussed for a taxi turn on ground maneuver. Furthermore, it will give a eneral overview of the AVF response to lateral maneuvers in general. inally, it presents the results for the lateral tests of the Objective Motion Cueing Test (OMCT) showing that, in general, the AVF is able to meet the requirements of the test

Flight Simulator Results Comparing Three Aircraft Configurations: Quasi-Static, Flexible and Extended Flexibility

Full motion flight simulators are quite commonly used to evaluate handling qualities of an aircraft taking into account its rigid body dynamic model. However, new design, seeking for optimized aerodynamics with high aspect ratios, light and slender wings, has included new issues in handling qualities analysis. In such aircraft, the effect of the aeroelastic modes has a potential to affect its handling qualities characteristics. In this case, these aspects have to be respected in the dynamic model as well as in the flight simulator and the cockpit vibration due to aeroelastic modes must be included in the analysis. In this work the impact of the aircraft flexibility on the handling qualities is investigated. Therefore, an aircraft with significant coupling between rigid body and aeroelastic dynamics is considered. A dynamic model of a flexible aircraft is used, the flight simulator is configured to include the vibration in the cockpit, a dedicated test procedure is proposed, maneuvers with experienced test pilots are executed and the resulting data are analyzed. The pilot evaluation considered the PIO scale. Additionally, to evaluate the aircraft-pilot coupling susceptibility, two additional scales, called Riding Qualities Rating scale (RQR) and Control Inputs Rating Scale (CIR), are introduced. At the end the pilot rates are correlated with the HQ criteria results and remarks made about impact of flexibility on the handling qualities and pilot performance

Simulating Flexible Aircraft in a Full Motion Simulator

Classical flight dynamics analyses and pilot-in-the-loop simulations are traditionally based on rigid-body aircraft models. The assumption of rigid aircraft is acceptable for classical aircraft designs. However, present ecological and economical constraints require modern passenger aircraft to become more efficient and reduce their emissions. This leads to optimized aircraft designs with light structures and high aspect ratios, which exhibit an increased aeroelastic flexibility. These modern more flexible aircraft do not necessarily allow the assumption of rigid-body modeling approaches anymore but require the inclusion of structural flexibility for flight dynamics analyses and handling qualities assessments. This also affects pilot-in-the-loop simulations in a full-motion simulator, where the consideration of structural flexibility is no common practice. The present paper describes the preparation of an extensive simulator campaign with a flexible aircraft. It addresses the question of how to integrate the oscillations resulting from the structural flexibility into the motion filter of the simulator to achieve a realistic feeling of the flexible modes

In-Flight Remote Sensing and Identification of Gusts, Turbulence, and Wake Vortices

In this paper, the in-flight remote sensing technologies are considered for two applications: active load alleviation of gust and turbulence and wake impact alleviation. The paper outlines the strong commonalities in terms of sensors and measurement post-processing algorithms and presents also the few differences and their consequences in terms of post-processing. The way the post-processing is being made is detailed before showing results for both applications based on a complete and coupled simulation (aircraft reaction due to disturbances and control inputs during the simulation is influencing the sensor measurements)

Integration of Wake Impact Alleviation Control System into Control System Architecture of Modern Fly-by-Wire Aircraft

Wake vortices can represent a serious disturbance for encountering aircraft because they can cause sudden, unexpected aircraft reactions like strong rolling motions. This paper presents a control system, called Online Wake Identification and Impact Alleviation (OWIDIA), which has the particular purpose to alleviate these wake-induced aircraft reactions and is applied in addition to the regular flight control laws of the aircraft. The OWIDIA system uses the information of an airborne forward-looking Doppler lidar sensor about the wake vortex wind velocities in front of the aircraft. On the basis of these measurements, an online wake identification algorithm characterizes a potential wake vortex and a control module determines the control surface deflections that countervail the wake-induced aircraft response. The present paper shows the undesired interactions that can occur when combining the OWIDIA system with the basic control laws of the aircraft and demonstrates how these interactions can be prevented

Deriving Lidar Sensor Requirements for Use in Wake Impact Alleviation Functions

The paper complements previous works of the authors on lidar-based active wake impact alleviation control functions by investigating the lidar sensor requirements for such systems. This control system can increase the safety during wake vortex encounters by preventing a dangerous sudden (in particular rolling) motion, which often characterizes wake-vortex encounters. Such technology could provide an opportunity to relax the current wake-vortex-based separation minima and thus lead to a capacity gain for airports and in the terminal area. The performance of this system obviously strongly depends on the performance of the lidar sensor, however in a nontrivial way. The direct problem, i.e. determining the system performance obtained with a given sensor configuration, already requires setting up a fully coupled simulation environment. The inverse problem, i.e. determining the best suited set of sensor parameters, is approached in this work through parameter variations and sensitivity studies. Key performance parameters for assessing the overall system performance, and providing trends for sensor requirements are defined. As for most technical systems, the best configurations are characterized by a good tradeoff of the relevant parameters, in this case field of view, measurement range, spatial resolution, and measurement noise. The coupled simulations revealed that, contrary to the authors' expectations, very good results were already obtained with small ranges of 60 m and lateral fields of view of +/- 16°

Flight dynamics simulation of formation flight for energy saving using LES-generated wake flow fields

Wake vortices are an inevitable result of lift generation and can pose a threat to any aircraft, which accidentally encounters the wake of another aircraft. However, wake vortices can also be used in a beneficial way. Due to its rotational direction, the air flows upwards outside of the vortex pair, giving additional energy to any aircraft located in these regions. This method of saving energy is used by migratory birds, resulting in these birds flying in typical V-formations. This study deals with the question, whether it is possible with a standard autopilot (without a dedicated formation flight mode) to keep the aircraft’s position accurately at a desired position in the wake flow field without accidentally encountering those areas of the wake where steady-state flight is impossible, even in the presence of atmospheric disturbances (e.g. turbulence) and fluctuating vortex core positions. For this purpose, simulations were performed applying three-dimensional flowfields generated with large eddy simulations. Here, even with young vortices, the target sweet spot position varies in the lateral and vertical directions with a magnitude of a few metres at a constant distance behind the generator aircraft. Hence, also the vortex-induced forces and moments change continuously while flying at the same relative position to the leading aircraft. Preliminary simulations with an A320 flying in the wake of an A340, utilizing the regular autopilot of the comprehensive DLR A320 flight simulation model without a dedicated formation-keeping mode, show that the autopilot does not accidentally encounter hazardous regions within the wake. This indicates that it could be sufficient for a formation-keeping autopilot for civil transport aircraft to be designed as the outer loop of the regular autopilot

In-Flight Remote Sensing and Characterization of Gusts, Turbulence, and Wake Vortices

In this paper, the in-flight remote sensing technologies are considered for two applications: active load alleviation of gust and turbulence and wake impact alleviation. The paper outlines the strong commonalities in terms of sensors and measurement post-processing algorithms and presents also the few differences and their consequences in terms of post-processing. The way the post-processing is being made is detailed before showing results for both applications based on a complete and coupled simulation (aircraft reaction due to disturbances and control inputs during the simulation is influencing the sensor measurements)