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Eric Nguyen-Van

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 Short Biography

Eric Nguyen-Van received the M.Sc. degree in mechanical engineering from École Polytechnique Fédérale de Lausanne, Switzerland in 2016.

His first contact with applied research was in 2015 within ABB Switzerland, Corporate Research, Dätwill, Switzerland, where he was involved in Airborne Wind Energy (AWE). His contributions to AWE were modeling and simulation of tethered gliders, and flight automation experiments.

Following this first experience in flight dynamics, he started in 2017 a PhD at ISAE-SUPAERO and ONERA, Toulouse, France, where his research now focuses on relaxing lateral static stability of transport aircraft without impacting controllability using distributed electric propulsion.

 Phd summary 

The pursuit of performances for transport aircraft can lead to question the rule stating that an aircraft must be statically stable. Latest civilian transport aircraft such as the A380 and A350 are designed to reduced longitudinal static stability. Though requiring an automatic stability augmentation system, it leads to a reduced horizontal stabilizer, a reduced wetted area and lower empty mass. However, the same cannot be applied for the vertical stabiliser because this one is essentially dimensioned by the One Engine Inoperative (OEI) case. This flight condition, requires a sufficiently large vertical tail to counter the yaw moment produced by the remaining engine. Because this case happens at low speed, the vertical stabiliser remains oversized for the rest of the aircraft operation.

A change of paradigm becomes possible with the emergence of new propulsion architecture and particularly Distributed Electric Propulsion (DEP). The idea has been suggested in the litterature that reduced lateral stability can be achieved with this type of propulsion. To this day, it was not demonstrated and no methodology has been proposed to dimension a vertical tail with DEP.

The objectives of this thesis are twofold :
1 - Propose a methodology for the co-design of vertical tail and control laws answering the constraints of safety, flight qualities and actuator limitations.
2 – Flight demonstration of a small scale demonstrator using DEP and reduced lateral stability.

The first idea consists in evaluating the possibility of reducing lateral static stability of aircraft with distributed electric propulsion through the study of flight envelop. A trimming tool adapted to aircraft with distributed propulsion and variable size vertical tail was developed to this end. Although based on simple physics, this tool was able to compare a traditional twin engine aircraft with an equivalent DEP aircraft from the point of view of stability.

A next part was to improve the fidelity of the modeled aircraft and specifically aero-propulsive interactions, which are often cited as non-negligeable forces at low speed for flight control. The idea was to adapt a technic to answer our needs and add it to the previous study to assess the sensitivity of stability in the presence of aero-propulsive interaction.

The configuration studied quickly brought us to question the existing regulation requirements to demonstrated safe operability of a DEP aircraft with reduced lateral stability. Knowing that these requirements are dimensioning for the vertical tail, we proposed to translate high level safety objectives into new requirements adapted to a DEP architecture.

The main principle behind co-design is the use of optimisation technics and include both control law gains and design parameters into the set of optimisation variables. This way, it is possible for automatic control to influence the design at an early phase. A known procedure to achieve this is to use H-infinite control design methods and multi-objective optimisation functions. The specificity of this study is that flight performance and handling quality are include in the co-design approach, both in nominal and OEI conditions such as to obtain an optimal design, answering all dimensioning cases.

Knowing the limitation of our models and the assumptions made for the co-design architecture, we thought about a mean of validation through flight tests. For this purpose a distributed electric propeller flight demonstrator model was built and flight tested. The model has a 2m wingspan, weights 8.25Kg and has eight engines distributed along the wing leading edge. Flight data were then used to identify a model of the aircraft, improve simulation models and our strategy for the co-design architecture.

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