Reducing aircraft stall speed of firefighting aircraft using retrofit vortex generators

The speed at which firefighting aircraft release their payload is a critical factor in the effectiveness of their use. This paper presents a retrofit modification that can be made to existing Air Tractor AT-802F firefighting aircraft used in Australia to increase their effectiveness by reducing the stall speed using low-profile, sub-boundary layer, vortex generators on the wing upper surface. A numerical optimization study was conducted using ANSYS FLUENT, where the lift coefficient of a NACA 4415 airfoil section was maximized at the stall angle for the plain airfoil. A 2-stage optimization process involving Kriging surrogate modeling and Particle Swarm Optimization (PSO) was applied to narrow the search space and then find the optimal location and dimensions of the micro Vortex Generators (VG). The final design yielded a 49% increase in the maximum lift coefficient of the airfoil and suggested that the commonly used evenly spaced VG pairs may not be the most effective arrangement.