STABILITY CONSIDERATIONS OF HIGH-LIFT DEVICES

Abstract

High Lift Devices (HLDs) are wing surfaces that change the aerodynamic characteristics for desirable performance in specific flight regimes. HLDs improve the slow flight performance and help reduce the stall speed by increasing maximum lift coefficient. When these devices are deployed, the force distribution over the airfoil is changed and the position of aerodynamic center is altered. The movement of aerodynamic center affects the stability characteristics of airplane due to change in moment magnitude. This research is aimed at finding the fundamental effects of high lift devices on stability characteristics of TC12 airfoil through Computational Fluid Dynamics. Stability derivatives are calculated for four different configurations: clean configuration, only slat deployed configuration, only flap deployed configuration and both slat and flap deployed configuration. The static and dynamic coefficients are validated for NACA 0012 by using forced oscillation technique and the results were compared with experimental data. Then the same methodology is applied for calculation of static and dynamic stability derivatives of TC12 airfoil for different high-lift configurations. Simulations were performed at various flight conditions in terms of angles of attack and oscillation amplitudes while keeping the air velocity constant. This approach enabled the efficient and accurate computation of stability derivatives. The results derived for static stability coefficients are linked with the flow physics. HLDs deployment have positive effect on the static stability if the flow remains attached to airfoil during oscillation. Flow separation and vortex shedding makes the high-lift airfoil statically unstable. Dynamic stability coefficients are positive for all configurations showing that perturbation will not damp out.