Morphlight theory inspired by raptor: bionic design and experimental study of the morphing flight vehicle MorphSteppe inspired by the Aquila nipalensis

Abstract Bird forelimbs exhibit complex flight kinematics, including wing morphing and flapping motions with angle asymmetry. However, data on angle-asymmetric flapping in birds are scarce, and well-established theories and methods remain limited. Motivated by this challenge, we present a biofeature reconstruction method of the Morphlight theory that integrates high-speed videography with millimeter resolution 3D scanning to better approximate these kinematic features. Frame-by-frame analysis of Aquila nipalensis wingbeat sequences quantified joint rotations with angle-asymmetric, after which a three-rod Tang model and corresponding flapping equation of the Morphlight theory were formulated to predict the rotational angles of the wing joints. The bird’s wings were then scanned to obtain key aerofoil profiles, which were used to construct a bionic airfoil incorporating the secondary remiges. Guided by the measured kinematics, we designed the drive mechanism and implemented a sliding crank–rocker mechanism to realize angle-asymmetric motion during the upstroke and downstroke. The resulting morphing flight vehicle MorphSteppe achieves high biofidelity in both wing geometry and angle-asymmetric flapping kinematics. Both flapping tests without inflow and outdoor flapping experiments were conducted to evaluate the aerodynamic performance and controllability of the morphing flight vehicle. The proposed Morphlight theory inspired by raptor, provides a generalizable framework for high biofidelity design of bird morphing flight vehicle that couples biological morphology with angle-asymmetric flapping kinematics.