IFASD2024 Paper Submission & Registration
17 – 21 June 2024, The Hague, The Netherlands

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09:40   Aeroservoelasticity 1
Chair: Rafael Palacios
30 mins
Wind Law Proposal for Aircraft Control in Turbulence
Abstract: In the frame of the “Aircraft Control in Turbulence” this article is highlighting an innovative methodology for the passenger’s comfort improvement and aircraft dynamic loads reduction. Actually, this methodology has been developed by using the linear “Quasi-static” short period model and lies in the coupling of the lift and pitching moment equations. This coupling has been made possible by the analytical “Aerodynamic Crossed-Products” identification based on the Doublet Lattice method in the low frequency domain, even though never mentioned in flight mechanics handbooks. Then, based on this preliminary analytical identification, this coupling led to a unique equation, seen as energetical type and named “Fundamental Equation of Aircraft’s Dynamic” or “Equation of Conservation”. This fundamental equation, at the heart of the Aircraft’s Dynamic, is a function of the flight mechanics parameters such as, the angle of attack derivative, the pitch rate and the pitch rate derivative, but also a function of several fundamental aerodynamic “Neutral points” which are governing the global Dynamic Aircraft response. In a first step, this equation has been highlighted with only the elevators and ailerons control surfaces for basic control laws tuning and then in a second step, the wind effect has been introduced leading to the fundamental equation with both control surfaces and wind effect as model inputs. Finally, it has been possible to define a global control surfaces order that enables to minimize the wind effect in the aircraft dynamic response. In a first part, this article presents the “keys steps” of the theoretical development leading to the “Fundamental Equation of Aircraft’s Dynamic in Turbulence”. In a second part, this concept is illustrated by the linear short period model time responses, with a focus on load factor time histories. This preliminary study constitutes a first step towards a more realistic approach and more complex simulations by considering on one hand an aeroelastic model with rigid and flexible modes and on the other hand by defining this specific control law in turbulence accounting for actuators characteristics, time delays.
30 mins
Passive and active load alleviation technologies for UHARW wings
Francesco Toffol
Abstract: In the framework of the Ultra High Aspect Ratio Wing Advanced Research and Designs (U-HARWARD) CS2JU founded project, different gust load alleviation (GLA) technologies were developed and studied. GLA is a key enabler for the development of new generation UHARW, indeed the GLA allows to limit the gust loads and as a direct consequence it can reduce the structural weight of the wing itself, and considering the snowball effect of the entire aircraft. This overall weight reduction improves the global aircraft efficiency allowing an increase in the aspect ratio. GLA technologies can be divided into two main categories: the passive ones where no action is needed to reduce the load and the active ones where a control system modifies the aerodynamic loads automatically. In this case, the passive GLA is performed with a Folding Wing Tip (FWT) developed by the University of Bristol and the GLA is performed with a Static Output Feedback controller developed by Politecnico di Milano. Both cases are compared with the baseline aircraft. A flutter assessment is performed to prove that the FWT do not introduces aeroelastic instabilities and the aircraft is flutter free across the entire flight envelope. A comprehensive comparison of the load envelopes obtained is provided, considering almost 2000 load cases for different flight points and mass configurations for the baseline aircraft and the GLA solutions. The gust cases are compliant with CS25 regulations and account for positive and negative cases, providing the bending-torsion envelopes in different spanwise placed monitoring stations. Thanks to NeOPT it was possible to realize a hybrid FEM model of the aircraft, where the wingbox is modelled with a detailed GFEM while the other components are modelled as stick elements. This model was used to perform linear gust analyses in Nastran with the hinge locked and released. The results of this HI-FI structural solution are used to compare the wing failure indexes in the two conditions, assessing the effectiveness of the GLA.

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