This thesis has two objectives: First, to investigate the behavior of typical twin engine commercial transport aircraft in ground effect under a wide range of conditions and geometry variations at the request of an aerospace company. And secondly, to add to the body of existing scientific knowledge on ground effect.In order to identify the opportunities for adding scientific knowledge, first a literature study was conducted. The conclusion of this study proved that there is insufficient research literature available on wing-bodies in the ground effect to answer the investigation launched by the aerospace company.A methodology was chosen to fulfill both objectives, namely generating ground effect performance data by means of CFD (Computational Fluid Dynamics) computations. The results are validated using existing wind tunnel measurements.It was determined which data points had to be calculated to cover the parameter space and it was established that the required effort could be completed within the time frame of this thesis. The landing high-lift configuration was the principal configuration to be investigated. Using this baseline, the impact of the following changes on ground effect performance were determined: a) changes to the high lift settings b) change to the engine thrust setting c) changes to landing gear deployment d) changes to the nacelle size e) changes to the wingtip geometry. After completing the calculation of all data points, it was also possible to develop a method that will enable engineers to calculate the effect of incremental changes in geometry and configuration, required for the initial stages of aircraft design.The main conclusions in order of importance are:For low to moderate angle of attack α, the ground effect is beneficial. Lift is increased by up to 3.5% of the total lift, drag is reduced by up to 33% of the total drag.However, as α>8.0°, the ground effect becomes less beneficial and the ground effect can even be detrimental, leading to a loss of lift of up to 5.5% while still having a drag benefit of up to 33%. The agreement between windtunnel data and CFD calculations is within 0.4% accuracy for the lift, and within 1.5% of the total drag value, except at the extreme case at moderate to high α and very close distance to the ground. Some of the differences can be explained in terms of practical problems in simulating the ground boundary conditions in the wind tunnel.The impact from a change to high lift setting and a change to thrust setting are most significant, with changes of up by up to 2% of total lift and up to 3.2% of total drag.There is a smaller but still quantifiable impact from the gear effect and the nacelle effect.A change to wing tip geometry has a minor impact on ground effect behavior, as lift is changed by up to 0.26% of total lift, only between 10.0°≤α≤12.0°.