Birdlike Takeoff Strategies Enabled by Flapping-Pitch Effect in a Meter-Scale Flapping-Wing Robot.

The takeoff strategy in birds involves a fundamental trade-off between acceleration and climb, yet its physical consequences are difficult to isolate in biological experiments. Here, we develop a meter-scale flapping-wing robot for controlled investigation of takeoff strategies. We show that a flapping-pitch effect, arising from flapping kinematics and aeroelastic interactions, enables pitch modulation at low speeds where conventional control surfaces have limited authority. In parallel, we establish a lattice-Boltzmann-method (LBM)-based 2-way fluid-structure interaction (FSI) framework for the full-process simulation of flapping-wing takeoff. To the best of our knowledge, this is the first LBM-based 2-way FSI analysis that resolves the complete takeoff dynamics of a meter-scale flapping-wing robotic system. Under the tested conditions, the 15° low-angle strategy increased the total flight distance by 49% relative to that of the 65° strategy and reached a comparable altitude at the 3-s evaluation time. These results provide engineering-based physical evidence that may help interpret certain avian takeoff strategies and highlight the role of the flapping-pitch effect in low-speed flight control.