This paper is the Part I of a parametric study on CFJ airfoils. A trade study is performed for a series of CFJ airfoils based on the NACA 23121 airfoil on the injection location, suction location, suction size, angle of attack (AoA), momuntum coefficient, airfoil thickness, Reynolds number and their resulting effects on the lift, drag, moment and energy consumption. The two dimensional flow is simulated using steady and unsteady Reynolds Average Navier-Stokes (RANS). A 5th order WENO scheme for the inviscid flux, a 4th order central differencing model for the viscous terms and the one equation Spalart-Allmaras turbulence model are used. The Mach number is 0.15 and Reynolds number is 6.4 × 106. CFJ airfoils are shown to be effective at increasing the lift and reducing the drag drastically. The jet location and the AoA are found to be influential parameters for the energy consumption and aerodynamic efficiency. The pitch-down moment and energy consumption are reduced when the suction is located more upstream. The lift and drag are improved when the suction is located more downstream. The pumping power decreases when the AoA is increased before the apparition of a recirculation region. When the AoA is further increased, the energy consumption is increased because of the increased jet total pressure losses due to the strong adverse pressure gradient and separated flow.