Performance-based Wing Design Including Environmental Sustainability Issues

The paper presents recent advances in the development of a formulation for multidisciplinary robust design optimization (RDO) of aircraft structures under environmental requirements. Specifically, the performances of a environment friendly (with respect to fuel burn and acoustic emissions) wing are analyzed in different operating conditions such as cruise or approach. Such a wing is characterized by a high efficiency, resulting in a low thrust required (with low fuel burn and low engine noise) and by a low generation of airframe noise. When dealing with long (or extended) range aircraft, the evaluation of the fuel consumption is greatly affected by the cruise segment and, therefore, by the aircraft performance in cruise condition (generally characterized by high speed and altitude); on the other hand, community noise considerations pertain all those operations characterized by low altitude and (since dealing with civil applications) low flight speed, such as approach/landing and take-off. The first aim of this paper is to analyze the performance of the wing in both cruise condition, and take off and landing, focusing the attention on the total aircraft life-cycle-cost. The second goal of the present work is the identification of a suitable objective function able to take into account the overall aircraft performances in terms of environmental sustainability and economical re- bounds. This objective function has to lead to a robust design with respect to different operating conditions and applications. It will be shown how the most likely application (in terms, e.g., of distance to cover) of the airplane will affect the optimal solution. The overall problem is embedded in a formulation for multidisciplinary design optimization for conceptual design (MDO-CD) of aircraft comprising models for structures, aerodynamics, aeroelasticity, flight mechanics and propulsion, along with semi-empirical models for aeroacoustics and life-cycle cost models. The optimal design (in terms of wing-plant geometry and structural characteristics) is evaluated as that which maximize the expected value of the aircraft performance, suitably defined. Range, cruise speed, payload and procedural parameters (such as glide/climb angle and speed) may be taken into account by means of their probabilistic distribution. The constraints used for the analysis are structural (maximum shear and normal stress), aeroelastic (minimum flutter and divergence speed) and pertaining the static and dynamic equilibrium of the aircraft in the different operating conditions. Finally, a sequential quadratic programming algorithm is used for the constrained design optimization, being the expectation of the overall aircraft performance the function to maximize.