Proceeding of the 2008 International Joint Conference in Engineering IJSE2008, August 4-5, Jakarta, Indonesia Combined Chordwise and Spanwise Effects Acting on a Wing Near the Ground Sridhar Ravi*, Hadi Winarto†, Robert Carrese# ,Zayd Louli§ *† School of Aerospace Mechanical and Manufacturing Engineering Royal Melbourne Institute of Technology, Bundoora 3083, Australia Tel.61-3-99256019, email: Sridhar.Ravi@rmit.edu.au ; Hadi.Winarto@rmit.edu.au §#email: Carrese7@hotmail.com ; ZLouli@qinetiq.com.au Abstract– It is well known that an aircraft experiences increasing lift and decreasing drag as it approaches the runway during landing. Therefore the aerodynamic efficiency of an aircraft, represented by its lift to drag ratio, increases considerably if it flies close to the ground [1] . This fact has been taken advantage of, particularly in the design of WIG (Wing in Ground) Effect Crafts [2] . Most articles concerned with WIG effect usually discuss the chordwise and the spanwise effects separately [3, 4] . The increase in lift is attributed to chordwise effect, whereas the decrease in induced drag is attributed to spanwise effect. In reality the chordwise and spanwise effects interact non-linearly. This interaction results on the wing’s lift and drag having different values from those predicted by the individual effects considered separately. This paper describes the aerodynamic analysis of a wing, taking into account both chordwise and spanwise effects simultaneously. The computer program is based on Numeric Lifting Line Theory [5, 6] , where the solution is obtained iteratively rather than by assuming a lift distribution approximated by a Fourier Series and then solving the resulting system of equations simultaneously. Furthermore, the magnitude of the lift at each spanwise location on the wing is calculated taking into account the effect of wing’s height above the surface. The ground effect is modeled by using image vortices located below the ground plane. Both lumped vortex and vortex panel methods with Neumann boundary conditions are used for the potential flow simulation, which is corrected for viscous effect using boundary layer integral approach. Keywords: Ground Effect, Aerodynamic Efficiency, Numeric Lifting Line theory, Vortex Panel Method I. INTRODUCTION round effect is a phenomenon that both fixed wing as well as rotary wing vehicles experience, when in close proximity to ground or water surface. The induced drag experienced by a wing is observed to decrease significantly as it approaches a solid surface. A remarkable increase in lift is also noticed, which leads to a very high aerodynamic efficiency or lift to drag ratio, L/D, much higher than if the wing is in a free stream. For example, Rozhdestvensky [2] stated that the WIG craft Aerocon Dash 1.6 has a calculated value of free stream L/D of 15, whereas at the condition of extreme ground effect it has an L/D of greater than 32. It is even said that the success of the Wright Brothers first flight was partially due to the ground effect. WIG craft may be considered as a boat that can travel much faster than a normal boat because it is actually flying above the water surface. On the other hand, it may be considered as an aircraft that has a much higher aerodynamic efficiency because it takes advantage of the wing in ground effect as stated earlier. The speed of a WIG craft is similar to that of a helicopter, but its cost of operation is very much lower. It is for those reasons that WIG craft has a special niche among the various available modes of transport. However, there still exist a number of unsolved technological problems, such that presently the application of the ground effect is mainly still limited to small sport and recreational crafts or the more secretive military experimental vehicles. Earlier WIG craft design works had been carried out mainly in Russia and Germany, even though other countries such as the United States, China and Japan, were also involved in the development of this technology. More recently a number of companies like Wiget Works [7] in Singapore and companies in Korea have looked to exploit this specialized transportation market, which is definitely always searching for more efficient means of travel. Theoretical analysis of ground effect phenomena has been carried out for a long time. For example, Wieselsberger [4] wrote an article on this topic in 1922. Due to the great difficulty in finding the solution to the mathematical problem posed by this phenomenon, it was necessary to make certain simplifying assumptions. The reduction in induced drag was considered to be a span-wise effect. The wing tip trailing vortices strengths were not as strong as in the free stream case, due to the fact that the trailing vortices were not free to form but confined G