Jana Ehlers

Airborne Doppler LiDAR Sensor Parameter Analysis for Wake Vortex Impact Alleviation Purposes

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.

Wake Impact Alleviation Control Based on Wake Identification

During a wake-vortex encounter, an aircraft can experience significant attitude and flight-path changes, which can represent a severe safety risk. 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 light detection and ranging (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. Because of the integration of the identification algorithm, it is possible to apply the wake impact alleviation with LIDAR sensors restricted to line-of-sight measurement...

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.

Verification of a Flying Wing Handling Qualities Analysis by means of In-Flight Simulation

*† ‡ The assurance of appropriate handling qualities represents a critical aspect for the development of a flying wing. This paper presents an analysis and evaluation of the handling qualities of a flying wing configuration for 750 passengers. Its flying qualities are evaluated by applying analytical handing qualities criteria. These criteria are however developed for conventional airplanes and imply that the longitudinal and lateral motion of the aircraft can approximately be considered as separate motions. As the considered flying wing configuration does not fulfill the prerequisite of an approximately decoupled lateral and longitudinal motion the applicability of the analytical criteria is not guaranteed and the additional evaluation of the handling qualities by pilots is absolutely required for such an aircraft. For this purpose an in-flight simulation is carried out with the DLR research aircraft ATTAS which is able to simulate other airplane configurations during flight. It allows analyzing the flight dynamics of the flying wing under real flight conditions and an evaluation of its handling qualities by test pilots. The flight tests are performed with the original baseline-configuration of the flying wing and a modified configuration with active control which is examined to evaluate the potential of flight control augmentation to improve the handling qualities. The maneuvers of the flight tests focus on the examination of the dynamics of the flying wing during turns. Thanks to the means of in-flight simulation it is possible to evaluate the unusual coupling of the lateral and longitudinal motion of the aircraft. The analyses permit to point out some major deficiencies in the handling qualities of the considered flying wing.