2009 Brazilian Symposium on Aerospace Eng. & Applications 3 rd CTA-DLR Workshop on Data Analysis & Flight Control Copyright © 2009 by AAB September 14-16, 2009, S. J. Campos, SP, Brazil AERODYNAMIC ANALYSIS OF THE USE OF MULTI-WINGLETS IN LIGHT AIRCRAFTS Catalano, F. M., catalano@sc.usp.br Cosin, R., renatocosin@uol.com.br Aerodynamic Laboratory – São Carlos Engineering School – University of São Paulo – São Paulo – Brazil Abstract. The major objective of this work is to analyse the aerodynamic characteristics of multi-winglets aplied to light aircrafts. This wing tip device has demostrated a potencial of improving the aerodynamic eficiency of aircrafts by the reduction on the induced drag. The data discussed were resuslts of experimental investigations for a wing-body half model at Re= 4×10 5 with six diferent multi-winglet configurations plus the base line. It was achieved up to 7.3% of increase on maximum aerodynamic efficiecy and even greater values for others medium to high lift coefficient regimes.A performance analysis was also conducted revealing a potencial increase of 12% on maximum climb ratio.The pressure dustribution over the wing was mesured, leading to conclusions about the global and local efects of the device on the wing loading. A wake study from a sevem hole pitot probe mapping downstream the wing and structural loading investigation complete this reserch. Keywords: multi-winglets, induced drag, tip sails, aerodynamic efficiency 1. INTRODUCTION The now days major requirements of an aircraft lead to the necessity of more efficiency. On this contest, the drag reduction plays a central role for the success of an airplane either on accomplishing its mission or on commercial aspects. In this scenario, the scope of this study is to investigate the potential use of multi-winglets to enhance the efficiency and performance or aircraft by reducing the induced drag. Generating lift on a finite wing implies on the presence of the wing tip vortex as an unavoidable collateral effect that reduces the lift of the wing and generate a significant amount of drag, particularly known as induced drag. It has been proven that modifications on the wing tip or the use of wing tip devices can reduce in expressive amounts the induced drag, improving the wing efficiency. Extensive investigations have been conducted with the objective of studying these devices, as well proposing new design and approaches. Modifications of the wing tip can either move the vortices away in relation to the aircraft longitudinal axis or reduce their intensity (Kravchenco,1996). Some of these devices such as winglets, (Whitcomb,1976), tip-sails (Spillman, 1978), (Spillman and McVitie, 1984), (Spillman,1987) and multi-winglets ,(Smith and Komerath,2001), take advantage of the spiraling airflow in this region to create an additional traction, and reducing the induced drag. Whitcomb [3] showed that winglets could increase wing efficiency by 9% and reduce induced drag by 20%. Other devices break up the vortices into several parts, each with less intensity facilitating dispersion, which is important, for instance, for the decrease of the interval time between takeoff and landings in large airports (La Roche and Palffy,1996). (Kravchenco,1996) tested and compared different shapes of wing tips: winglets and tip-sails. The winglets presented higher aerodynamics benefits up to Mach 1.0, however they also presented structural problems for the aircraft due to the increase in bending moment at the wing root. Tip-sails, at low lift coefficient, provided the same benefits; nevertheless, the bending moment at the wing root was less. Research with agricultural aircraft has also been made comparing wing-tip devices, (Coimbra, R and Catalano, 1999). For this category of aircraft, besides both aerodynamic and structural advantages, the influence of the vortices created during the mission of the aircraft is an added parameter in the analysis. Winglets have been used to improve sailplane performance. (Smith and Komerath,2001) mentions the development work on winglets for sailplanes tested in a wind tunnel with scale models. 2. EXPERIMENTAL CONFIGURATION The tests were carried out in the LAE 2 closed circuit low speed wind tunnel, with a turbulence level of 0.25% at 30m/s. The test section has 1.7 m of width, 1.3 m of height and 3.6m of length,(Catalano,2001). The Reynolds number used was Re=4×10 5 except for the wake measures which was conducted with Re=3×10 5 . 2.1. General model characteristics For the present research, was designed and built a half model based on a high wing single engine trainer aircraft under development on Engineering School of São Carlos. The model consists on a wing-body configuration with 1:6 scale. The wing has no taper nor sweep. The dihedral is 1.5° and the washout is 1.25°. It was used the NACA 23015 airfoil in the entire span and the full span aspect ratio is 8.