Dietrich Fischenberg

Wake Encounter Flight Control Assistance Based on Forward-Looking Measurement Processing

Weather dependent delays, incidents and even accidents play an important role in aircraft operation. Any airplane is subject to air motion. Thus, turbulence is an important parameter in aeronautics. The phenomena which are summarized as gusts and turbulence strongly affect the passenger comfort and the safety of aircraft. Especially the turbulence caused by the wake of other aircraft can cause undesired motions mainly roll and vertical displacements. Active control technology can be applied to alleviate wake vortex effects on aircraft and support the pilot to carry out his control task. With the aid of specific controllers such vortices can be safely encountered even if the required control power temporarily exceeds the available capacity. Aircraft equipped with such a controller will be less affected by unforeseen wake vortex encounters or even will be able to follow another aircraft closer than authorized by the current separation distances without any compromise concerning safety. A very promising concept for wake vortex disturbance alleviation is the feed-forward disturbance compensation. The application of such an approach requires the accurate determination of the flow disturbance to calculate the necessary counter measures in terms of required control activities. Thus, the disturbance flow determination plays an important role and needs to be investigated thoroughly. Modern LIDAR technology has the potential to measure the flow filed in front of the aircraft and to provide the required disturbance information in advance before it affects the aircraft. The final goal of the DLR approach is the development of an Integrated Ride and Loads Improvement System (IRLIS) which is able to cope with the whole frequency range of atmospheric flow disturbances relevant for aircraft operation. The presented paper will summarize the status of the work performed during the last years and the current activities.

Wake Encounter Severity Assessment Based on Validated Aerodynamic Interaction Models

Wake encounter severity criteria based on validated models are of great importance for any wake vortex related severity assessment. The aerodynamic interaction model “strip method” describes the vortex-induced aircraft reaction. The model quality is validated with wake encounter flight test data. Model shortcomings are improved with dedicated refinements. A simplified hazard area approach is developed employing validated simulation models. With one simple criterion, the roll control ratio, safe and undisturbed flight operations can be ensured. A limit value for manually flown (non fly-by-wire) aircraft is derived from piloted trials. With the simplified hazard area prediction method, this can be universally applied for wake vortex advisory systems like DLR’s wake vortex prediction and monitoring system.

Wake Identification Based Wake Impact Alleviation Control

During a wake vortex encounter an aircraft is exposed to strong unsteady disturbance velocities which can lead to significant changes in the aircraft attitude and flight path. This can represent a severe safety risk and can result in injuries to the passengers and crew as well as damages to the aircraft. The application of a wake impact alleviation control system can considerably decrease the aircraft’s response during the wake encounter, and hence diminish the pilot workload while reducing the potential risk to the passengers, crew, and aircraft. The realization of a wake impact alleviation controller presented here is based on a forward-looking LiDAR sensor. The information about the disturbance velocities in front of the aircraft is used to determine the control surface deflections that compensate the wake-induced disturbance moments. The novel approach of this concept is the combination of the wake impact alleviation system with a wake identification algorithm. Due to the integration of the identification algorithm it is possible to apply the wake impact alleviation with LiDAR sensors restricted to line-of-sight measurements only. In this case the LiDAR sensor only detects the flow velocity in the direction of the measurement beam. A measurement of the full velocity vector of the flow field upstream of the aircraft, which LiDAR sensors of the foreseeable future will most likely be unable to provide, is not necessary for this approach. The wake identification based wake impact alleviation is assessed for different encounter scenarios and a brief sensitivity study is performed for the most important parameters of the wake identification. It is shown that the wake impact alleviation control system significantly reduces the wake-induced attitude change of the aircraft and thus represents a promising concept to increase safety during wake vortex encounters.