In this paper, 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 postprocessing. 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). The performances in terms of wind reconstruction quality for the gust/turbulence case and in terms of wake impact alleviation performance for the wake vortex case are shown based on simulations and are very promising.

This paper presents an overview of the DLR activities on active load alleviation in the CleanSky Smart Fixed Wing Aircraft project. The investigations followed two main research directions: the multi-objective, multimodel, structured controller design for the feedback load alleviation part and the use of Doppler LIDAR technologies for gust/turbulence anticipation. On this latter topic, the prior work made in the AWIATOR European FP6 project constituted a reference in terms of demonstrations and the objective was not to repeat these previous investigations with a real sensor in flight test but to develop new ideas for the exploitation of the Doppler LIDAR measurements for gust alleviation purposes. Very fruitful exchanges between industry partners and research organizations took place during this project and all the work presented in this paper has been made using a generic long-range benchmark provided by Airbus on the basis of the XRF-1 model.

This paper presents a sensitivity study of a wake vortex impact alleviation system based on an airborne forward-looking Doppler LiDAR sensor. The basic principle of the system is to use this sensor to measure the wind remotely ahead of the aircraft. On the basis of these measurements the system estimates whether a wake vortex is located in front of the aircraft. If this is the case, the wake vortex characteristics are identified and the control deflections countervailing the wake-induced aircraft response are computed and applied. An integrated simulation environment comprising a full nonlinear 6-DoF A320 model (with control laws), wake vortex models, and the wake impact alleviation algorithms was developed. The LiDAR sensor subsystem has many design parameters that influence the overall performance in a complex way, which makes it difficult to derive adequate requirements. The presented parameter study provides first insights into the role of each parameter as well as some adequate parameter combinations.

Perform measurements at different locations  different line-of-sight directions "Simple" scan geometry based on a cone of revolution

Most of the gust load alleviation systems (GLAS) of currently-operational aircraft are of feedback-only control architecture based on inertial measurements. In few other aircraft, aerodynamic measurements from air data sensors are additionally included, or presently considered for inclusion, as they usually result in improving the performance of the GLAS. In both sensor types, the control system has very little time to react; and therefore, the performance of the GLAS would be further enhanced if the turbulence or gust could be measured at some distance ahead of the aircraft. Doppler LIDAR (LIght Detection And Ranging) sensors could enable such preview of the turbulence or gust, at a short range (typically between 30 and 200 meters) ahead of the aircraft. In this paper, the availability of a vertical wind profile ahead of the aircraft is assumed, and the paper focuses on the design of a load alleviation controller that exploits this information. The proposed methodology of designing this controller is based on the application of the H ∞ optimal control techniques to a discrete-time preview control problem. Minimizing the H ∞ norm of the transfer function from wind input to loads output, directly leads to the design of an effective load alleviation function. The preview-control formulation enables the design algorithm to synthesize a combined preview-capable feedforward and feedback load alleviation function. For a practical reason, the developed methodology is applied in the course of this paper to a flexible sailplane model (DLR's Discus-2c), although it is intended to be applied to larger airplanes (e.g. transport airplanes and business jets).