Journal - The Institution of Engineers, Malaysia (Vol. 66, No. 4, December 2005) 1 DRAG REDUCTION IN AIRCRAFT MODEL USING ELLIPTICAL WINGLET Prithvi Raj Arora 1 , A. Hossain 1 , Prasetyo Edi 1 , A.A. Jaafar 1 , Thamir S. Younis 2 and M. Saleem 1 1 Department of Aerospace Engineering, Universiti Putra Malaysia, 43400 UPM, Serdang, Selangor 2 Department of Mechanical Engineering, Universiti Putra Malaysia, 43400 UPM, Serdang, Selangor ABSTRACT Aerodynamic characteristics for the aircraft model with NACA (National Advisory Committee for Aeronautics) wing No. 65- 3-218 have been studied using subsonic wind tunnel of 1000 mm x 1000 mm rectangular test section and 2500 mm long of Aerodynamics Laboratory Faculty of Engineering (Universiti Putra Malaysia). Six components wind tunnel balance is used for measuring lift, drag and pitching moment. Tests are conducted on the aircraft model with and without winglet of two configurations at Reynolds numbers 1.7 x 10 5 , 2.1 x 10 5 , and 2.5 x 10 5 . Lift curve slope increases more with the addition of the elliptical winglet and at the same time the drag decreases more for the aircraft model with elliptical shaped winglet giving an edge over the aircraft model without winglet as far as Lift/Drag ratio for the elliptical winglet is considered. Elliptical winglet of configuration 2 (Winglet inclination 60 0 ) has, overall, the best performance, giving about 6% increase in lift curve slope as compared to without winglet and it is giving the best lift/drag ratio. Keywords : Induced Drag, Lift Curve Slope, Wind Tunnel Balance, Winglet INTRODUCTION The aerodynamic efficiency and drag of aircraft wing shapes depend on profile drag as well as on the induced drag. By introducing various types of wingtip devices in wingtip region the aerodynamic efficiency of existing and advanced aircraft can be improved and thereby their operational capabilities can be enhanced. The idea behind all the wingtip devices is to diffuse the strong vortices released at the tip and optimise the span wise lift distribution, while maintaining the additional moments on the wing within certain limits. For this purpose one should be able to produce favorable effects of the flow field using wing tip and reducing the strength of the trailing vortex with the aid of wingtip devices, e.g., winglets, wing tips of complex plan-form, sails, and various modifications of the wingtip side edge. Modern interest in winglets spans the last 25 years. In July 1976, Whitcomb[1-2] of NASA Langely Research Centre published a general design approach that summarised the aerodynamic technology involved in winglet design. Small and nearly vertical fins were installed on wings of KC-135A aircraft and flight was tested in 1979 and 1980. Whitcomb showed that winglets could increase an aircraft’s range by as much as seven percent at cruise speeds. A NACA contract [3] in the 1980s assessed winglets and other drag reduction devices, and they found that wingtip devices (winglet, feathers, sails, etc.) could improve drag due to lift efficiency by 10 to 15% if they are designed as an integral part of the wing. The “spiroid” wingtip [4] produces a reduction in induced drag at the same time blended winglet [5] reduces drag by eliminating the discontinuity between the wing tip and the winglet. A smoothed version is used on the gently upswept winglet of the Boeing 737-400. Boeing Business Jets and Aviation Partners, Inc. have embarked upon a cooperative program to market conventional winglets for retrofiting to the Boeing 7xx series of jetliners. Flight tests on the Boeing Business Jet 737-400 resulted in a 7% drag reduction. Theoretical predictions had indicated that the configuration would have only a 1-2% improvement, and wind tunnel tests had shown only 2% drag reduction [6]. This indicates that wind tunnel test results of winglet configurations should be reviewed with some caution. The first industrial application of the winglet concept was in sailplane. The Pennsylvania State University (PSU) 94-097 airfoil has been designed for use on winglets of high- performance sailplanes [7]. To validate the design tools, as well as the design itself, the airfoil was tested in the Pennsylvania State Low-Speed, Low-Turbulence Wind Tunnel from Reynolds numbers of 2.4 x 10 5 to 1.0 x 10 6 . Performance predictions from two well-known computer codes are compared to the data NOMENCLATURE c Airfoil chord (m) α Angle-of-attack ( ˚ ) D Drag force (N) L Lift force (N) M Pitching moment (Nm) ρ ∞ Air density (kg/m 3 ) S Reference area (m 2 ) V ∞ Free stream velocity (m/s) q ∞ Dynamic pressure (Pa) C D Drag coefficient C L Lift coefficient C M Pitching moment coefficient C1 Load No. 1 C2 Load No. 2 C3 Load No. 3 C4 Load No. 4 C5 Load No. 5 C6 Load No. 6 001-008•drag reduction 3/19/06 12:54 PM Page 1