To evaluate the propulsion system capabilities of a Flapping Micro Air Vehicle (FMAV), a new aeroelastic model of a typical flexible FMAV is developed, utilizing the Euler–Bernoulli torsion beam and quasi steady aerodynamic model. The new model accounts for all existing complex interactions between the mass, inertia, elastic properties, aerodynamic loading, flapping amplitude and frequency of the FMAV, as well as the effects of several geometric and design parameters. To validate the proposed theoretical model, a typical FMAV, as well as an instrumented test stand for the online measurement of forces, flapping angle and power consumption, has been constructed. The experimental results are initially utilized to validate the flight dynamic model, and several appropriate conclusions are drawn. The model is subsequently used to demonstrate the flapping propulsion characteristics of the FMAV via simulation. Using dimensionless parameters, a set of new aeroelastic coordinates are introduced. In this reduced design space, new generalized performance curves have been deduced. The results indicate that by proper adjustment of the wing stiffness parameter, as a function of reduced frequency, the FMAV will attain its optimum propulsive efficiency. This fact raises additional ideas of utilizing intelligent variable stiffness materials and/or an active morphing technology for the sustained flight of FMAVs.