Efficiency of Buoyancy Force Generation in a Pump-Based Buoyancy Engine for a Small-Scale Underwater Glider

Underwater gliders rely on buoyancy-based propulsion for energy-efficient and long-duration exploration, yet the efficiency of pump-driven buoyancy engines in small-scale systems remains insufficiently understood. This study aimed to evaluate the efficiency, repeatability, and stability of a pump-based buoyancy engine for a scaled underwater glider. A laboratory-scale glider model equipped with a pump-driven fluid transfer system was constructed and tested under controlled buoyancy states. Key performance indicators included servo displacement time, fractional volume of displaced water, average velocity, buoyancy efficiency, and platform stability. Results showed a strong linear relationship between servo displacement time and displaced volume, confirming precise and repeatable buoyancy control. Increasing the displaced volume from 60% to 80% improved the average velocity by 33% and buoyancy efficiency by 41%. Stability analysis indicated that the glider maintained consistent pitch and roll angles during buoyancy transitions, although larger displacements induced greater fluctuations due to longer motor operation and hydrodynamic resistance. These findings demonstrate that optimizing displaced volume is essential to balance velocity and stability in small-scale designs. The study contributes novel experimental evidence on buoyancy-based propulsion and provides a foundation for future work on scalability toward larger gliders and longer-duration missions.