The thin airfoil theory is reviewed pointing there is no impediment considering a thin airfoil in a non-uniform flowfield. This can be worked on by the Leading-edgesuction-parameter modulated Discrete Vortex Method (LDVM) to obtain an accurate unsteady solution, at low Reynolds number, when the flow is detached. Considering the example of the aerodynamic response of a flat plate encountering a large amplitude sharp-edged gust, we compare predictions from this method with the reference theory, simulations results and the experimental data from literature.