Importance of Translational Velocity for Bird-scale Flapping Wing Vehicles Incapable of Hovering

There exist multiple types of flyers in the world that either achieve lift through leveraging aerodynamics by cleverly choosing the wing airfoils of an airplane, or by flapping their wings. As the flapping wing vehicles (FWVs) decrease in scale, lift is predominantly generated by flapping. However, bigger birds or bird-scale flapping wing vehicle (BFWV) may not be able to hover but leverage the forward velocity to augment the lift generation. In this paper, we analyze the aerodynamic lift augmentation through the translational velocity for a 12g, BFWV with tail (flapping around 14 Hz). We prove that the vehicle is unable to hover, but there exist a significant augmentation through the translational motion. A cycle-averaged aerodynamic model including the contribution from the translational velocity is proposed, and experimentally validated. Finally, the analysis of the sufficient conditions on the velocity direction and orientation are studied to maintain the zero angular moment forward flight.