Miguel Silvestre

Evaluation of a Variable-Span Morphing Wing for a Small UAV

This paper describes the development and ground validation of a variable-span morphing wing intended be fitted to a small UAV prototype. The vehicle flies in the speed range 11m/s to 40m/s. The wing model is designed with the help of graphical CAD/CAM tools and then a full scale prototype is built for preliminary bench testing the wing/actuator system. The wing is built in composite materials and is made of two parts. The inboard part is fixed to the fuselage and uses a monocoque skin construction. The outboard part slides inside the inboard part to change the span of the wing and uses a typical structure made of spar, ribs and thin skin. An electro-mechanical actuation mechanism is developed using an aluminum rack and pinion system driven by two servomotors placed at center of the wings. Bench tests, performed to evaluate wing under load, showed that the system is capable of performing the required extension/retraction cycles and is suitable to be installed on a small UAV prototype.

Experimental Study of Instabilities and Secondary Effects of a Ground Vortex Flow

Laser-Doppler measurements of velocity characteristics of the flowfield resulting from the collision of a wall jet with a boundary layer are presented and discussed together with visualization of the flow. The experiments have been carried out for boundary layer to wall jet velocity ratios of 0.5 and 0.58. Direct photography, digital film imaging, and mean and turbulent laser Doppler measurements were obtained to characterize this type of flows. For the present conditions the results revealed the existence of a small counter-rotating recirculating zone located upstream the separation point not yet reported before for this type of flows. The results show that this secondary vortex has a similar oscillating behavior observed in some configurations leading to ground vortex flows, where they are also probably present, but due the geometric and characteristic parameters could not be identified separately. A particular ordered sequence was recognized for the small recirculation zone, and can be confirmed by the bimodal histogram of the horizontal velocity measurements obtained. In spite of the apparent organized sequence of the turbulent structure of the collision zone, the power spectra measurements did not exhibit any evident particular peaks.

A comparison of post-stall models extended for propeller performance prediction

Purpose The purpose of the paper is to analyse different post-stall models, originally developed for use in wind turbine codes, and extend their use to the propeller performance prediction. Design/methodology/approach Different post-stall methods available in the literature were implemented in JBLADE software. JBLADE contains an improved version of Blade Element Momentum theory, and it is appropriate for the design and analysis of different propellers in off-design conditions. Findings The preliminary analysis of the results shows that the propeller performance prediction can be improved using these implemented post-stall models. However, there is a lack of accuracy in the performance prediction of some propellers. Further comparisons including distribution of forces along the blade may help to better understand this inaccuracy of the models, and it will be studied in future work. Originality/value The work has extended the use of the post-stall models to the propeller performance prediction codes. It is shown that these models can be used to obtain an improved prediction of the propeller’s performance.

Multidisciplinary and Multilevel Aircraft Design Methodology Using Enhanced Collaborative Optimization

Since aircraft design is an inherently multidisciplinary undertaking, the quest for increasingly optimized solutions can only be comprehensively successful by implementing multilevel or system design optimization architectures to step up disciplinary optimizations. In this study, a methodology which uses the Enhanced Collaborative Optimization (ECO) multilevel architecture with the purpose of developing a multidisciplinary design optimization methodology within the context of the preliminary design stage of unmanned aerial vehicles is presented. The concepts of weighting coefficient and dynamic compatibility parameter are presented and assessed for the ECO architecture. A routine that calculates the aircraft performance for the mission profile and vehicle’s performance metrics under consideration has been implemented using low fidelity models for the aerodynamics, stability, propulsion, weight, balance and flight performance. A benchmarking case study of two different mission profiles for evaluating the advantage of using a variable span wing within the optimization methodology developed is also featured.

Visualization of a Ground Vortex Flow

Flow visualization results are presented for a highly curved flow resulting from the collision of plane turbulent wall jet with a boundary layer. This configuration can be found in the case of impinging jets of a V/STOL aircraft operating in ground vicinity. The experiments were carried out for wall jet to boundary layer velocity ratio of 1.57. The present results revealed the existence of two small vortexes located in the collision zone, that exhibit an unsteady behaviour.