Aircraft Wing with Advanced Technology Operation
AWIATOR is a multilateral technology platform funded by the European Commission under the Competitive & Sustainable Growth Area of the 5th Framework Programme. The aim of this project is to contribute to a new future aircraft design by applying and integrating new technologies in the fields of noise regulation, demand in passenger comfort on aircraft level and alleviation of structural loads due to aircraft manoeuvres and wind turbulence. AWIATOR will thus contribute to a higher performance of future aircraft. The institute, in cooperation with the Institute of Flight Systems, is involved in the development of new control strategies for Gust Load Alleviation. The development of these strategies is specially focused on the integration of new direct-lift control devices (mini-TEDs) and a LIDAR forward-looking sensor for determination of wind turbulences ahead of the aircraft, which are available on the AWIATOR test aircraft.
Gust Computation System (GCS)
To integrate the LIDAR forward-looking sensor in a control architecture, an algorithm for on-line estimation of turbulence was developed and flight tested. From the output of the forward-looking sensor and the inertial data, the GCS calculates the vertical wind angle of attack, which serves as an input for the Gust Load Alleviation System (GLAS).The GCS consists of two blocks, one for signal conditioning and one for gust computation. The signal conditioning block performs a synchronization of all the input signals which have different time delays and are differently filtered. The gust computation block calculates the wind angle of attack from flight mechanic relations. Furthermore, the GCS includes a Kalman filter for estimation of the vertical speed of the aircraft and additional filters to alleviate bias and noise errors.
Gust Load Alleviation System (GLAS)
Using the wind information from the GCS, a feed-forward gust load alleviation system based on a rigid aircraft model was designed (GLAS (rigid)) and validated with simulations on linear flexible aircraft models. This system was mainly based on earlier developments for the ATTAS aircraft and should serve as a reference for new developments.
The validation of the GLAS (rigid) showed no good performance due to the slow actuator dynamics of the test aircraft. The main problem was the delayed reaction of the actuators, yielding a bad synchronization of the aileron and mini-TED deflections with the wind at the aircraft wing. One simple solution to the problem is to make use of the fact that the wind reaching the aircraft is known in advance (forward-looking sensor). Hence the deflection of the control surfaces is started in advance to counteract the slow actuator dynamics. To determine this desired "pre-deflection" time, the optimization tool MOPS from DLR was employed. With this tool the reduction of the vertical aircraft acceleration over all possible "pre-deflection" times was optimized and a "pre-deflection" time of about 190ms was obtained. NB, this time is almost independent of the flight case and the continuous turbulence that was used, i.e. this time mainly depends on the actuator dynamics. Simulations with the modified GLAS (rigid) show the expected results concerning the reduction of vertical aircraft acceleration nz and wing root bending moment Mx. Both can be reduced by about 50% which is a very good improvement in terms of passenger comfort and load reduction.
Based on GLAS (rigid), the Institute of Robotics and Mechatronics developed a new controller (GLAS (flex)), which also takes into account the flexibility of the aircraft. The goal is to avoid the excitation of the wing root bending mode, thus reducing the loads on the wing. The GLAS (flex) incorporates the GLAS (rigid) system and an additional controller acting on the external ailerons of the aircraft. The improvement of GLAS (flex) (Mx reduced by more than 80%), compared to GLAS (rigid) and the open-loop aircraft without controller, can be seen in the simulation results for Mx, where theoscillations due to the wing root bending mode are almost fully alleviated.