The accurate prediction of flutter speed of an aeroelastic system is challenging. Flutter is a dynamic instability observed in flexible structures such as aircraft wings, tall chimneys, and long-span bridges. This dynamic instability originates from the interaction of aerodynamic, elastic and inertia forces. There exist various types of flutter mechanisms. The one treated in this thesis is the coalescence flutter, which is characterized by the coupling of two degrees of freedom. In turn, this coupling enables a net energy transfer from the flow to the structures. There are very few experimental approaches that closely estimate the flutter speed of complicated structures such as aircraft and long-span bridges. One particular approach is Zimmerman and Weissenburger flutter margin method. The crux of the method lies in the prediction of flutter onset using pre-flutter flight test data.