Flapping Hydrofoil Propulsion for Uncrewed Surface Vehicles: Design and Experimental Evaluation

This study presents a novel hydrofoil-based propulsion system for water surface-operating robots, inspired by the paddling locomotion of aquatic species. Several hydrofoil designs were developed and evaluated using a custom Hydroflapper setup to assess their hydrodynamic performance. The proposed framework incorporates a camber-modulating mechanism to investigate whether dynamic camber variation can enhance thrust and propulsion efficiency. Initial simulations indicated that camber modulation increases horizontal thrust compared to symmetric hydrofoils, highlighting its potential benefits. A physical prototype was then constructed, featuring independent control of heave and pitch motions. Indoor and outdoor experiments were conducted to measure thrust generation and efficiency under various hydrofoil geometries and operating conditions, benchmarking results against conventional propeller-based systems. Experimental findings show that symmetric hydrofoils exhibit higher efficiency than propeller-driven systems in starting from rest conditions, while camber-changing hydrofoils demonstrated reduced performance at the tested scale - likely due to mechanical limitations in the actuation mechanism. Complementary CFX simulations supported these results, showing minor efficiency gains for the cambered foils and suggesting that observed inefficiencies originate from mechanical rather than hydrodynamic constraints.