Frederico Afonso

Multidisciplinary Performance Based Optimization of Morphing Aircraft

Nowadays the aeronautic industry is battling with contradictory requirements. In one hand, there is the need to increase speed and capacity, while, on the other hand, there is an increasing need to minimize the environmental impact caused by air travel. The permanent need to improve aircraft performance and efficiency, have impelled not only the use of new aircraft configuration, but also the introduction of morphing solutions on the existing configurations. In order to achieve the optimal aircraft configuration or the best morphing solution for a determined mission, it is necessary to explore Multidisciplinary Design Optimization (MDO) solutions in the research and development process. A MDO framework is being developed for preliminary design and analysis of novel conjurations, including the capability to analyze morphing solutions. This tool was developed to be both modular and versatile, allowing the user to create custom plug-in like modules to tailor the software to each users needs. In this framework, the main aircraft disciplines are integrated with optimization software in a single optimization statement. With computational efficiency in mind, surrogate models of the disciplines are built and the quality of these approximation models is verified. Disciplines can be replaced by corresponding existing or pre-calculated databases. This work is being developed within the EU 7th Framework Project NOVEMOR, which has two main objectives: novel configurations and morphing solutions assessment. Firstly, for a conventional regional jet it is assessed the benefits of introducing a morphing wingtip for three different flight conditions. Secondly, morphing bending and twist controls were applied to a reference joined-wing configuration to improve lateral-directional stability.

The effect of stiffness and geometric parameters on the nonlinear aeroelastic performance of high aspect ratio wings

The increase in wing aspect ratio is gaining interest among aircraft designers in conventional and joined-wing configurations due to the higher lift-to-drag ratios and longer ranges. However, current transport aircraft have relatively small aspect ratios due their increased structural stiffness. The more flexible the wing is more prone to higher deflections under the same operating condition, which may result in a geometrical nonlinear behavior. This nonlinear effect can lead to the occurrence of aeroelastic instabilities such as flutter sooner than in an equivalent stiffer wing. In this work, the effect of important stiffness (inertia ratio and torsional stiffness) and geometric (sweep and dihedral angles) design parameters on aeroelastic performance of a rectangular high aspect ratio wing model is assessed. The torsional stiffness was observed to present a higher influence on the flutter speed than the inertia ratio. Here, the decrease of the inertia ratio and the increase of the torsional stiffness results in higher flutter and divergence speeds. With respect to the geometric parameters, it was observed that neither the sweep angle nor the dihedral angle variations caused a substantial influence on the flutter speed, which is mainly supported by the resulting smaller variations in torsion and bending stiffness due to the geometric changes.

Aeroelastic Analysis of High Apect Ratio Wings

The aeronautical industry is currently facing the simultaneous and conflicting demand to enhance flight efficiency while reducing emissions. One potential solution for reducing fuel consumption is to increase the wing aspect-ratio as it improves the lift-to-drag ratio. However, higher aspect-ratio wings result in higher deflections which in turn may lead to non-linear aeroelastic behaviour. In this work, the aeroelastic behaviour of a conventional regional aircraft with high aspect-ratio wings is investigated. The structural design aims to ensure that the wing is able to withstand a load limit of 3.8g. Aeroelastically scaled models using two classical scaling methodologies have been evaluated and compared. The two methodologies use scaling factors derived from the governing aeroelastic equations of motion. The first methodology consists of a direct modal response matching, while the second method uncouples the mass and stiffness distribution to achieve the modal response. The scaled structure design parameters are optimized to obtain the target scaled values. Also, an alternative non-linear aeroelastic scaling methodology using equivalent static loads is presented, which uses two different optimization routines to match the non-linear static response and the mode shapes of the full model. The results show a good agreement between the full-scale and reduced-scale models.