XIX CONGRESSO NAZIONALE AIDAA 17-21 settembre 2007 FORLÌ (FC) DESIGN OF MULTIPLE WINGLETS TO IMPROVE TURNING AND SOARING CHARACTERISTICS OF ANGELO D’ARRIGO’S HANG- GLIDER: NUMERICAL AND EXPERIMENTAL INVESTIGATION D. P. COIRO, F. NICOLOSI , F. SCHERILLO, U. MAISTO Dipartimento di Ingegneria Aerospaziale(DIAS), Università degl Studi di Napoli Federico II, Napoli, ADAG research group (Aircraft Design and Aeroflightdynamics Group); www.dpa.unina.it/adag ABSTRACT The main aim of the present paper is to investigate the influence of multiple winglets on hang-glider climbing performance. The study aims to optimize the CL3/2/CD parameter. The investigation was performed both numerically and experimentally starting from airfoils and winglet shape design. Given the shape of a real hang- glider wing under aerodynamic load the first phase of the work concerned the main geometric characteristics of winglet design : number of winglets, airfoils, planform shape, twist. A 3D wing model was built and using the indications obtained from the design, different sets of winglets were built. The wing model was built to enable winglets to be applied to the wing tip without changing the wing span and aspect ratio. The tests carried out on the hang glider model showed an improvement in wing performance of about 15%. However, the model reproduced a full scale wing flying under aerodynamic load and, according to the model builders, it showed a positive twist angle (leading edge up). This could mean that the winglets were more efficient because the original wing showed a strong tip vortex, A new model wing with an elliptical planform was therefore built to verify this further. The test results on the elliptical wing did not show the same improvement in performance obtained with the hang glider model. Nevertheless, compared to the original elliptical wing an improvement was still found. 1. INTRODUCTION Ever since man started to think about flying, he has striven to imitate the shape and structure of a bird wing . Large soaring birds like the Peruvian condors, are able to soar at very high altitudes in very narrow thermals and this is probably in part due to their tip feathers called remiges. These are continuously moved and adapted to optimize flying under different flight conditions. Nowadays, composite materials, such as epoxy carbon fibers, allow very stiff structures to be built, even slender shapes like remiges. The first investigations on a single winglet were performed by Whitcomb [1],[2] in the mid 1970s and it was shown that, if properly designed, the winglet can improve efficiency by reducing the induced drag. Many other researchers have investigated their behavior, designing winglets for commercial and general aviation aircraft as well as for sailplanes [3].. Furthermore, the added friction and interference drag has to be cancelled out by the forward thrust generated by the winglet lift. Since this has been proven to work, it is thus possible to extend this concept to multiple winglets. The principle is to spread the tip vortex in more vortices of less intesity. A variety of types of multiple winglets have been investigated by many authors in the past, such as, Spillman [4],[5] , , Zimmer [6], La Roche [7], and more recently by Smith [8], [9] and Catalano [10]. The importance of numerical accuracy and the difficulties in predicting the effect of winglets on drag using numerical methods have been well illustrated by Smith [11]. Different concepts, including box and ring wings, have been thoroughly analyzed by Kroo [12]. The main goal of this work is to investigate the influence of multiple winglets on the climbing performance of a hang glider. To this end, a set of winglets was designed and tested for application onto a hang-glider wing tip. As shown by Smith [8] ,[9] and Catalano [10], it appears that by using an opportunely designed set of remiges it is possible to improve wing performance by minimizing the hang-glider sink rateV s (1). This is inversely proportional to the endurance parameter CL 3/2 /CD. The main objective of this work is to improve this parameter. 85/08 74 Aerotecnica Missili e Spazio Vol. 87 2/2008