ICAS 2000 CONGRESS 771.1 AN EXPERIMENTAL STUDY ON WINGTIP DEVICES FOR AGRICULTURAL AIRCRAFT Rogério F. F. Coimbra § and Fernando M. Catalano* Aircraft´s Laboratory, University of São Paulo, São Carlos, BRAZIL § Doctorate Student, University of São Paulo * Ph.D. Professor, University of São Paulo Abstract The induced drag is responsible for nearly 50% of aircraft total drag and can be reduced through modifications to the wing tip. Some models displace wingtips vortices outwards diminishing the induced drag. Concerning agricultural airplanes, wing tip vortex position is really important, while spreading products over a plantation. In this work, wind tunnel tests were made in order to study the influence in aerodynamic characteristics and vortex position, over Brazilian agricultural aircraft, by the following types of wing tips: delta tip, winglet and down curved. The down curved tip was better for total drag reduction, but not good referring to vortex position. The delta tip gave moderate improvement on aerodynamic characteristic and on vortex position. The winglet had a better vortex position and lift increment, but caused an undesirable result referring to the wing root bending moment. However, winglet showed better development potential for agricultural aircraft. Nomenclature ASEF aerodynamic-structural efficiency factor, ASEF = ∆E f / ∆M b AR wing aspect ratio b wing span b T wing tip span c wing chord C D drag coefficient C Dmin minimum drag coefficient C L lift coefficient C Lmax maximum lift coefficient dC L /dα wing lift curve slope (dC L /dα) ∞ wing profile lift curve slope Di induced drag e Oswald efficiency factor L lift L/b wing span loading L/D aerodynamic efficiency (L/D) b basic wing aerodynamic efficiency M b wing configuration root bending moment M b b basic wing root bending moment α wing angle of attack or incidence ∆E f wing configuration aerodynamic efficiency factor, ∆E f = (L/D)/(L/D) b ∆M b wing configuration root bending moment factor, ∆M b = M b /M b b ϕ lift curve slope ratio, ϕ = (dC L /dα) ∞ /(dC L /dα) 1 Introduction With the increasing need for fuel economy, all possible areas of drag reduction need to be investigated. A form which offers considerable promise is the induced drag. Induced drag is associated with the shedding of vorticity along the span of a finite lifting wing and, in particular, in the wingtip region. For most subsonic airplane configurations, induced drag contributes nearly 50% of the total drag in optimum cruising flight and contributes much more than 50% of the total drag in climbing