978-1-4799-6062-0/14/$31.00©2014 IEEE Experimental Investigation of an Aircraft Wing Model Using Slotted Winglet Rajesh Nandi, Md. Assad-Uz-Zaman, Md. Fazle Rabbi, Mohammad Mashud * Department of Mechanical Engineering Khulna University of Engineering & Technology Khulna-9203, Bangladesh * Corresponding author: mdmashud@yahoo.com Abstract—this work represents the aerodynamic features for aircraft wing model with and without slotted winglet. When an aircraft moves forward with a high speed then a small circulatory motion of air is created at the wingtip due to the difference in pressure between the upper and lower surface of the wing is called vortices. This circulatory fluid tends to leak at the wingtip from lower to upper surface of wing which causes downward motion is called “downwash” and generates a component of the local lift vector in the direction of the free stream called induced drag. Downwash causes reduction of lift and contribute induced drag to the total drag. Reduction in drag reduces fuel consumption, increases operational range, increases endurance and increases achievable speeds. An experimental study is accompanied to test the potentiality of slotted winglet for the reduction of induced drag, and for the improvement of lift coefficient without increasing the span of aircraft wing. The model composed of a swept wing built from NACA 0012 airfoil. The test conducted in subsonic wind tunnel of 1m×1m rectangular test section at flow speed 25m/s placing the wing without winglet, wing with winglet at 30° inclination, wing with winglet at 60° inclination, and wing with winglet at 70° inclination at angle of attack ranging from 0 to 16 degree. The test result shows use of slotted winglet reduces drag coefficient by 20-25% and increases lift coefficient by 10-20%. Keywords— Airfoil, induced drag, Wind tunnel, Winglet I. INTRODUCTION From the very beginning of think about flying, man has striven to imitate the shape and structure of a bird wing. The researchers start to look at the flying characteristics of soaring birds such as eagles, condors, hawks, vultures, and ospreys etc. All of these birds has “pin” feathers at the ends of wings that produce slotted wingtips. They found this pin feathers of birds worked to reduce drag, as well as being used to provide roll control, in the same manner as ailerons on aircraft. The requirements of many modern aircraft missions are such that high values of aerodynamic efficiency must be obtained with aircraft having wings of relatively restricted length of span [1]. The drag that the aircraft produces limit the performance of an aircraft. This drag stems out from the vortices shed by an aircraft’s wing, which induces a downward component of air velocity and generated a component of the local lift force in the direction of the free stream called induced drag. The amount of drag the aircraft induces can be reduced by modifying wingtips which force the vortices farther apart from wingtip and at the same time create vortices with large core radii. Lesser the drag an aero plane experience lesser the power i.e. lesser the fuel require to fly an certain distance, thus making flight, more efficient and less costly [2]. There are many drag reduction device and winglet is one of the promising drag reduction device. Winglets reduce induce drag by reducing wingtip vortices, the twin tornados formed by the difference in pressure between the upper surface and lower surface of an airplane's wing by reducing span wise flow. The wingtips vortices are unavoidable byproducts by the lift presence, so it means that the difficulties associated with force that support the aircraft in the air. Induced drag is a consequence of these wingtips vortices. Induced drag is responsible for approximately 30% on entire drag in cruise conditions and also 50% in high-lift conditions. Modern interest in winglets spans the last 25 years. Richard Whitcomb used small and nearly vertical fins installed on a KC-135A and flight was tested in 1979 and 1980 [3-4]. He showed that winglets could increase an aircraft’s range by as much as seven percent at cruise speeds. In 1980s a NASA contract [5] 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. Robert Jones investigated the advantages of single winglets for small transports, on which they can provide 10% reduction in induced drag compared with elliptical wings. Now most new transports are being incorporated with winglets, including the Gulfstream III and IV business jets, the Boeing 747-400 and McDonnell Douglas MD-11 airliners, and the McDonnell Douglas C-17 military transport. The first industry application of the winglet concept was in sailplane. The Pennsylvania State University (PSU) 94-097 airfoil had been designed for use on winglets of high-performance sailplanes [6]. The airfoil was tested in the Penn State Low-Speed, Low-Turbulence wind tunnel to validate the design tool as well as the design itself. Experimental data were compared to the performance prediction from two well-known computer codes, and both were found in good agreement with the wind tunnel measurements. J. J. Spillman at the Cranfield Institute of technology in England [7], carried out another investigation on wingtip airfoils. Spillman investigated the use of one to four sails on the wingtip fuel tank of a Paris MS 760 Trainer