In PALAST active and passive load alleviation techniques were reviewed together. The passive measures required modification of the primary structure and thus influenced the dynamic response of the wing. An active load alleviation scheme for an aircraft was based on its static and dynamic structural behaviour. Therefore, a significant interaction of passive and active load alleviation technique was expected. Identification, analysis and optimisation of these effects were performed by a coupled flight-dynamic and aeroelastic simulation model with both load alleviation techniques implemented.
A baseline structural model was parameterised over multiple structural parameters, considering the composite layup of wing panels and stringers, which was normally employed for wingbox structural optimisation. This enabled a variable stiffness layout which may frequently be adapted in the analysis procedure. Finally, a structural optimisation task was performed, exploiting maximum efficiency of active and passive load alleviation.
PALAST enabled and developed technology for a multidisciplinary design approach, using combined active and passive load control. Taking into account all advantages of load alleviation, as well as possible detrimental interactions, a reasonable structural design with minimised weight can be achieved. Lightweight structural design takes a key role in reduction of fuel consumption and related CO2 emission, one of the “ACARE Vision 2020” goals.
Project PALAST was the result of a successful submission to a call for proposal topic within the CleanSky Joint Technology Initiative. This particular topic was included in the Smart Fixed Wing Aircraft (SFWA) programme and its call identifier was the following: SP1-JTI-CS-2010-05. This research framework had been created with the original purpose of pursuing additional research in terms of alleviation and control of loads acting on the wings of an aircraft.
Project PALAST had a total duration of 18 months (1.5 years), running from June 2011 until December 2012, and involved a group of researchers from different scientific areas, such as lightweight structures, flight dynamics and flight controls, from a single institution - the Technische Universität München. Two different institutes from this university had been in charge of the scientific work: the Institute of Lightweight Structures and the Institute of Flight System Dynamics. After the conclusion of the project, the total effort had been estimated to lie around the originally predicted 26 person-months.
The major challenge addressed throughout project PALAST had been the alleviation of gust loads acting on an aircraft wing by making use of active and passive strategies. Both of these techniques proved to be effective for the given aircraft configuration. The passive technique, which is named aeroelastic tailoring, had been successfully applied to the wing-box structure, and depending on the required aileron effectiveness, weight savings up to circa 40 % in the design zone could be achieved. On the other hand, active gust load alleviation had been applied primarily in terms of feed-forward control. Its application in a structural sizing approach generated a potential improvement of circa 30 % in terms of weight saving.