Ph.D. (Engg) : Autorotation of Single-Winged Spinning Samaras

Nature has consistently served as a powerful source of innovation, offering elegant and sustainable solutions to complex engineering problems. Among these, the spinning samara seed stands out as a biologically efficient system for passive aerial transport. Samaras, such as those from mahogany and Buddha coconut trees, exhibit stable autorotative descent, making them strong candidates for biomimicry in aerial delivery systems. Understanding and replicating the flight mechanics of samaras requires accurate analytical modelling. The dynamics of a single-winged spinning samara can be described using Newton’s laws and Euler’s rigid‐body equations, while the aerodynamic forces acting on the wing can be derived from the Navier–Stokes equations or using Blade Element Momentum Theory (BEMT). Together, these frameworks provide a foundation for predicting its motion, thrust generation, and stability in samara-inspired designs. Building on this theoretical basis, the present thesis delivers a comprehensive experimental study on the bioinspired engineering of single-winged spinning samaras, focusing on their aerodynamic behavior, kinematic characteristics, structural morphology, and wake dynamics. To investigate the kinematics, a custom-designed drop rig was developed to capture high-resolution visual data of the steady-state descent. Parameters such as descent velocity, coning angle, wingtip trajectory, and precession were extracted and analyzed. The results revealed a complex motion involving coupled coning and precession, challenging simplified theoretical models that typically assume a steady, non-precessing descent. Parallel morphological studies using high-resolution 3D scanning of natural samaras highlighted spanwise variations in chord length, camber, and sweep, which contribute significantly to aerodynamic performance. Five 3D printed models incorporating geometric variations were fabricated to evaluate their aerodynamic efficiency. Experimental observations showed that models featuring variable chord, sweep, and anhedral/dihedral configurations achieved the lowest descent velocities, underscoring the importance of structural morphology in enhancing autorotative performance. To examine local flow physics in detail, a custom low-Reynolds-number vertical wind tunnel was developed and characterized. Flat-plate airfoils were studied using Particle Image Velocimetry (PIV) across a wide range of angles of attack and Reynolds numbers, revealing flow regimes ranging from steady attached flow to unsteady vortex shedding. Wake flow physics of samaras were further captured within a transparent glass chamber using seeded PIV, revealing stable wingtip vortices extending several diameters downstream and confirming the presence of a windmill-brake state analogous to helicopter autorotation. Induced velocities computed using Momentum Theory showed close agreement with theoretical predictions. To evaluate practical feasibility, a bioinspired delivery system was designed and tested through drone-based release experiments. Six models (FR01 to FR06) were fabricated and deployed under varying payloads and wind conditions. All models demonstrated successful autorotation and stable descent, confirming the viability of samara-inspired mechanisms for passive aerial delivery. This research advances the understanding of samara aerodynamics and opens pathways for bioinspired applications in unmanned aerial systems. Future work should explore 3D motion capture, high-fidelity simulations, and optimization of geometries and materials. The insights from this thesis provide a strong foundation for future innovations in samara-inspired flight technologies.

Speaker :  G.YOGESHWARAN

Research Supervisor: Gopalan Jagadeesh

Co-Research Supervisor: Srisha Rao M V