American Institute of Aeronautics and Astronautics 092407 1 An Investigation into the Aerodynamic Efficiency of Tailless Aircraft Aliya Valiyff 1 and Maziar Arjomandi 2 The University of Adelaide, Adelaide, South Australia, 5005 From the perspective of aerodynamics, tailless aircraft are defended by many as potentially the most efficient aircraft configuration. The supporting argument being that the reduced surface area resulting from the tailless configuration directly results in reductions in drag. However, the efficiency of such configuration is realized through the utilization of active control systems. Without active control, the expected aerodynamic efficiency gains are partially or wholly negated by design compromises required to provide stability and control. The magnitude of washout required to stabilize such aircraft are usually quiet high, in the order of 8 to 10 degrees depending on the wing loading, airfoil type and control requirements of the aircraft. This high magnitude of wash out required dictates the lift distribution, such that only limited locations on the wing are flown at the design lift coefficient, thus increasing the associated induced drag. This paper discusses the efficiency of tailless configuration without active control and through the presentation of a case study undertaken with the use of both theoretical and empirical methods available proposes an all moving wing tip configuration as the design configuration of choice when considering tailless aircraft. Nomenclature A = aspect ratio S = wing planform area b = wing span c = chord length C D0 = zero angle of attack drag coefficient C Dinduced = induced drag coefficient of main wing C L = main wing lift coefficient C l = airfoil sectional lift coefficient C l = lift curve slope CM = main wing moment coefficient (quarter chord) Cm = aerofoil section moment coefficient (quarter chord) D = drag force  = angle of attack of main wing  = climb angle  = geometric twist of the wing  = taper ratio of the wing SM = aircraft static margin  1/4 = quarter chord sweep  1/2 = mid chord sweep X np = position of neutral point X cg = position of centre of gravity E = Jones edge velocity factor e = Oswald efficiency factor q = dynamic pressure 1 Undergraduate Student, School of Mechanical Engineering, The University of Adelaide, AIAA Student Member. 2 Lecturer, School of Mechanical Engineering, The University of Adelaide, AIAA Member. 47th AIAA Aerospace Sciences Meeting Including The New Horizons Forum and Aerospace Exposition 5 - 8 January 2009, Orlando, Florida AIAA 2009-1436 Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.