The current work delivers the effect of ground proximity on longitudinal aerodynamic forces and the elevator deflection required for trimming the aircraft. The academic understanding states that the with the increasing proximity to the ground,downwash progressively reduces.The methodology adopts the approximation of linear decrement for the estimation of the residual downwash at any height above ground within the unit wingspan. The proposed method utilizes non-dimensional height above ground for the approximation of effective downwash angle in the presence of ground. The approximately predicted effective downwash angle is subsequently utilized to estimate the effect of ground proximity on longitudinal forces, trim angle of attack, and elevator deflection required for trimming the aircraft. The behavior of estimated aerodynamic forces,i.e., lift and drag with the dimensionless height above ground is presented for displaying the variation of forces between outside and inside ground effect regime. The conventional method of estimating longitudinal aerodynamic forces during any flight phase employ equations of motion in terms of recorded flight data. A comparative analysis of longitudinal aerodynamic forces estimated by both methods is presented for assessing the efficacy of the proposed methodology.



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