Flapping-wing aerodynamic models that are accurate, computationally efficient and physically meaningful, are challenging to obtain. Such models are essential to design flapping-wing micro air vehicles and to develop advanced controllers enhancing the autonomy of such vehicles. In this work, a phenomenological model is developed for the time-resolved aerodynamic forces on clap-and-fling ornithopters. The model is based on quasi-steady theory and accounts for inertial, circulatory, added mass and viscous forces. It extends existing quasi-steady approaches by: including a fling circulation factor to account for unsteady wing–wing interaction, considering real platform-specific wing kinematics and different flight regimes. The model parameters are estimated from wind tunnel measurements conducted on a real test platform. Comparison to wind tunnel data shows that the model predicts the lift forces on the test platform accurately, and accounts for wing–wing interaction effectively. Additionally, validation tests with real free-flight data show that lift forces can be predicted with considerable accuracy in different flight regimes. The complete parameter-varying model represents a wide range of flight conditions, is computationally simple, physically meaningful and requires few measurements. It is therefore potentially useful for both control design and preliminary conceptual studies for developing new platforms. ... Read more

Different flapping wing micro aerial vehicles (FWMAV) have been developed for academic (Harvard’s RoboBee), military (Israel Aerospace Industries’ Butterfly) and technology demonstration (Aerovironment’s NanoHummingBird) purposes. Among these, theDelFly II is recognized as one of themost successful configurations of FWMAV, with a broad flight envelope, that spans fromhover to fast forward flight, revealing autonomous capabilities in the form of automatic flight and obstacle avoidance. Despite the technological development, very little is known about the dynamic behavior and aerodynamic force generation mechanisms of FWMAVs which, in turn, limits the development of models that could be used for advanced control strategies and flight simulations. The present dissertation contributes to the understanding of the mechanics of flapping flight, using a data-driven systematic approach to the modeling of the DelFly II. ... Read more

The determination of dynamic forces acting on a Flapping Wing Micro Aerial Vehicle (FWMAV) is a challenging task due to the unsteady nature of force generation mechanisms. To assure a proper force identification in future researches, this work compares two different methods to obtain the longitudinal forces acting on FWMAVs and discusses their applicability regions. The methods were 1) calculation of forces from the recordings of the FWMAV's position in a free flight condition; 2) direct force measurements in a tethered flight condition in a wind tunnel. The DelFly II is used as the FWMAV test platform in the measurements. During free flight experiments, its position and attitude were recorded at a rate of 200Hz using an external visual tracking system, whose acquired information was then analyzed to obtain the flight states and calculate the forces and moments that act on the platform during flight, under a set of kinematic assumptions. Subsequently, similar flight conditions were tested in the tethered situation. An ATI Nano-17 Titanium force transducer was used to measure time-resolved forces. The results for the most common flight regime of the DelFly, which is a slow forward flight at a high body pitch angle, are presented. It is shown that the tethered force balance tests agree with the free flight data when assessing the aerodynamic forces that are perpendicular to the stroke plane of the flapping wing. However, the forces that act along the stroke plane are coupled with structural dynamic terms, thus affecting the final lift and thrust identification. These results point to inadequate force identification in fixed point force measurements, due to effect the of the dynamic modes of the FWMAV body, thus advising proper cross-comparing between experimental methods. ... Read more